Royal-Royal Marriages Today

[Tatiana Maria]

Sometimes I saw people referring to her mother as Princess Olimpia Torlonia and sometimes as just Donna Olimpia, similar to Paula of Belgium.

​

Italian noble families frequently assumed unofficial titles for younger sons and daughters even if legally speaking the title was restricted to the eldest son. Thus, the future Queen Paola was technically only a member of a princely family and not a princess herself prior to the abolition of the Italian nobility in 1948, but she was sometimes unofficially known as Princess Paola Ruffo di Calabria.

Her mother is aristocratic so she is descending from aristocrats through her. But we are discussing royal/royal marriages here and from that she is far away, despite being the great-granddaughter of a spanish King.

Given that marriages to (upper-class) commoners with no particular royal or noble ancestry is now the norm for European royalty, though, I think it is reasonable to also classify marriages to nobles and other near-royals as exceptional in the same context.

 

[Somebody]

What might be a good match for Rafael, prince of Gran-Pára (born 24 April 1986). As the expected future head of the Brazilian imperial family he is expected to marry 'equally'. Any Roman Catholic royal princesses in their thirties that could be a good match?

Princess Luisa Maria of Belgium, archduchess of Austria-Este, is 9 years his junior (born 11 October 1995) but might be a good match and would fit all criteria.

And what about his younger sister, for her to remain in line to the (defunct) throne, she would also need to marry equally. Any Roman-Catholic princes in their late 30's (or early 40's) left? She herself was born in 1989.

Would the (four) sons of Luis María Gonzaga de Casanova-Cárdenas y Barón, Duke of Sántangelo, Grande of Spain, and Archduchess Monica of Habsburg/Austria qualify as 'equal'?
* Baltasar Carlos Casanova-Cárdenas y Habsburgo-Lorena (Vallfogona de Balaguer, 17 de agosto de 1981).
* Gabriel María Casanova-Cárdenas y Habsburgo-Lorena (Vallfogona de Balaguer, 21 de marzo de 1983)
* Rafael María Casanova-Cárdenas y Habsburgo-Lorena (Castillo de La Rápita, Vallfogona de Balaguer, 11 de agosto de 1986)
* Santiago Casanova-Cárdenas y Habsburgo-Lorena (Castillo de La Rápita, Vallfogona de Balaguer, 26 de abril de 1993)

 

[Muhler]

It would IMO not be far out if some of the Danish children fell in love and married a member of a noble family here, say the Ahlefeldts, Laurvigs or Scheel. They are all old noble and very wealthy families many of whom have been personal friends and even Ladies-in-Waiting for the DRF for at least a couple of generations now.
And given personal friendships, also among the children and age-wise, a marries between the younger siblings of King Frederik and Queen Mary could also end up marrying younger sibling(s) of the Dutch RF. Perhaps the Belgian or Spanish as well. - Not the Swedish though, too big an age-gap, except for perhaps Vincent and Estelle. And age-wise there is only Magnus in Norway to match Isabella.

Marriage between first cousins is likely to be banned in DK. Too many such marriages here among certain immigrants, carrying on such traditions for generations, with the result there are now being too many very accomplished banjo-players here... But you can't ban one segment of the population from marrying their first cousins and allowing other segments to do so.

 

[Linda_26]

And what about his younger sister, for her to remain in line to the (defunct) throne, she would also need to marry equally. Any Roman-Catholic princes in their late 30's (or early 40's) left? She herself was born in 1989.

Would the (four) sons of Luis María Gonzaga de Casanova-Cárdenas y Barón, Duke of Sántangelo, Grande of Spain, and Archduchess Monica of Habsburg/Austria qualify as 'equal'?
* Baltasar Carlos Casanova-Cárdenas y Habsburgo-Lorena (Vallfogona de Balaguer, 17 de agosto de 1981).
* Gabriel María Casanova-Cárdenas y Habsburgo-Lorena (Vallfogona de Balaguer, 21 de marzo de 1983)
* Rafael María Casanova-Cárdenas y Habsburgo-Lorena (Castillo de La Rápita, Vallfogona de Balaguer, 11 de agosto de 1986)
* Santiago Casanova-Cárdenas y Habsburgo-Lorena (Castillo de La Rápita, Vallfogona de Balaguer, 26 de abril de 1993)

I'm not sure if they would qualify as "equal", but two of them are already married and have children. Gabriel is married to Cristina Rodríguez y Gámez-Frauendorff, with whom he has two daughters, and Rafael is married to Nicole Lemann, and they have two children:
Descendants of Archduke Franz Karl of Austria

 

[eejm]

What about Ingrid Alexandra of Norway and Claus-Casimir of Nassau?

 

[Somebody]

What about Ingrid Alexandra of Norway and Claus-Casimir of Nassau?

Do you mean Count Claus of Orange-Nassau? I don't expect him to marry a royal bride. He is more likely to marry someone in the (old money) business community based on his social circles.

It would also be a surprise if Ingrid-Alexandra ends up marrying royalty or nobility but an uncontroversial spouse in the Norwegian royal family would be good for a change.

Count Felix of Montpezat would make an excellent groom for her. His second cousin Count Richard von Pfeil und Klein-Ellguth would also make an excellent royal groom (maybe for Amalia?) - a fun fact: Richard's grandparents met at the wedding of Amalia's grandparents.

 

[DaughterofFrance]

Here are more of my dream royal couples:

Prince Gabriel of Belgium:

Infanta Sofia
Lady Louise Windsor
Princess Isabella of Denmark

Princess Isabella of Denmark:

Prince Amyeric of Belgium
James, Earl of Wessex
Pablo Urdangarin y Borbon

Princess Josephine of Denmark:

Prince George of Wales
Hereditary Prince Jacques of Monaco


Infanta Sofia:

Prince Emmanuel of Belgium
James, Earl of Wessex
Crown Prince Christian
Count Felix of Mozpezat

Princess Eleonore of Belgium:

James, Earl of Wessex
Crown Prince Christian
Prince George of Wales

Princess Charlotte of Wales:

Prince Nicolas of Sweden
Prince Vincent of Denmark
Hereditary Prince Jacques of Monaco

I wrote this list for the people who are not expected to be monarchs in bolded.

 

[ronald biver]

I believe in reality, not in guessing and wishing who is to marry who in the royal family past & present, if it is officially broadcast to the press, then I would be happy or disappointed, and that is my opinion. After all I love surprises about happy announcements of royal births and relationships B/w nobilities & royalties.

 

[Hans-Rickard]

Given the close friendship between Haakon and Mette-Marit, and Prince Kyril of Bulgaria and Rosario Nadal, i cannot help but think about a possible match between Princess Ingrid Alexandra and Prince Tassilo…

A match with a guy from outside of the Nordic region would give the Norwegian RF a much needed vitamin injection….. And who would say no if that guy would be a royal too ?

For Belgium and Denmark (i knooow it’s unlikely but) the pictures of The Duchess of Brabant and Count Felix happily conversing when Christian turned 18 gave me ”thoughts”

 

[JR76]

Given the close friendship between Haakon and Mette-Marit, and Prince Kyril of Bulgaria and Rosario Nadal, i cannot help but think about a possible match between Princess Ingrid Alexandra and Prince Tassilo…

A match with a guy from outside of the Nordic region would give the Norwegian RF a much needed vitamin injection….. And who would say no if that guy would be a royal too ?

For Belgium and Denmark (i knooow it’s unlikely but) the pictures of The Duchess of Brabant and Count Felix happily conversing when Christian turned 18 gave me ”thoughts”

Felix marrying Elisabeth would be a match made in heaven but I've long believed that he'd be the perfect match for Ingrid. A Scandinavian match for any of their heirs would go down very well with the populations of all the Scandinavian monarchies.

 

[maria-olivia]

Royals will still marry rich and clever Ladies or Gentlemen .... Their Weddings are happy only 5 dicorces in 2024
There will be 4 Prince Consorts for Spain, Belgian , Norway and the Netherlands !

 

[duke of poliganc]

I know that it is a rumor that Princess Amalia is seeing the Bulgarian prince, but assuming a match would ever happen would they continue the tradition of incorporating the princess titles in the titles of their children like they did with

Wilhelmina and Juliana, who’s children had the German titles through their father?

​

 

[JR76]

I know that it is a rumor that Princess Amalia is seeing the Bulgarian prince, but assuming a match would ever happen would they continue the tradition of incorporating the princess titles in the titles of their children like they did with

Wilhelmina and Juliana, who’s children had the German titles through their father?

I don't see why not. Though if they did I'm sure it'd be the Saxon titles instead of the Bulgarian ones.

 

[maria-olivia]

3 Future Queens , is it better to marry a Communor or a Royal/Noble such as Guillaume of Luxembourg did.
For the moment they are too young and rumors are going .

 

[meeralakshmi]

Would love to see a marriage between two royals from different continents (that’s a genuine love match of course). I know some Spanish and Russian royals have married Georgian royals but Georgia is in both Europe and Asia. The dowager crown princess of Bulgaria married Prince Ghazi of Jordan recently but she isn’t a born royal, just a Spanish aristocrat. A marriage between a Japanese princess and a British prince would certainly get a lot of attention.

Not counting any of the marriages between Brazilian and European royals since the Brazilian royal family is a branch of the Portuguese royal family. Even a marriage between an East Asian and a Middle Eastern royal would be cool to see (or a marriage between two East Asian royals, it seems like the Middle Eastern royals are the only Asian royals who marry each other).

 

[JR76]

Not counting any of the marriages between Brazilian and European royals since the Brazilian royal family is a branch of the Portuguese royal family. Even a marriage between an East Asian and a Middle Eastern royal would be cool to see (or a marriage between two East Asian royals, it seems like the Middle Eastern royals are the only Asian royals who marry each other).

The Brazilian Prince João Maria of Orléans-Braganza married the Egyptian Princess Fatima Sherifa Chirine in 1949.

 

[meeralakshmi]

The Brazilian Prince João Maria of Orléans-Braganza married the Egyptian Princess Fatima Sherifa Chirine in 1949.

Oh wow that’s very cool.

After reading this, I'm immediately reminded that I ship her with Count Richard von Pfeil und Klein-Ellguth (Princess Benedikte of Denmark's oldest grandchild). He may not be royalty, but the ship's still interesting to think of, especially since he's a descendant of Queen Victoria of the UK and King Christian IX of Denmark, and the Dutch royals aren't descendants of either monarch.

Anyway, to get back on topic, what about dynastically equal marriages between royals from different continents? I know there aren't many Christian royal families outside Europe, but the ones that do occasionally spark my interest. What if by some fluke Prince George marries a Tongan princess, and his sister Charlotte in turn marries the Tongan crown prince's son? That would be fun to watch.

As for the present ones, chances are that we'll have to wait and see. I admit that it doesn't stop me from forming royal-royal ships in my head, such as Prince Constantine Alexios with either Infanta Maria Francisca or Princess Senate Mohato Seeiso of Lesotho. I also have some bizarre ships, such as Crown Prince Hussein of Jordan with Princess Maria-Olympia before the latter started dating Peregrine.

The first child of Princess Alix of Luxembourg, the 14th prince of Ligne, married Princess Eleonora of Brazil. His younger sister Princess Christine of Ligne married his wife’s older brother the Prince Imperial of Brazil. The princesses ended up as consorts of each other’s non-reigning royal families and the children of the two couples are double first cousins. Sadly Antônio passed away last year.

If there are any blue-eyed princesses born circa 2006, then one of them for future emperor Hisahito of Japan, in the hopes that Hiranuma Takeo (the politician who stated prior to Hisahito's birth that "If Aiko becomes the reigning empress, and gets involved with a blue-eyed foreigner while studying abroad and marries him, their child may be the emperor. We should never let that happen") will be asked to comment.

Guess he can marry Leonor then, wonder what would happen if that were to occur. The idea of a Japanese king/prince consort of Spain is quite interesting (that seems more likely than Japan accepting a foreign empress). Or maybe they would actually be allowed to be monarchs of their own countries and consorts of each other’s (oldest son would succeed to the Japanese throne and the oldest other child would succeed to the Spanish one).

If Aiko wants to remain royal after she marries she can marry a prince from another country (surprised that no Japanese princesses have done so). Here are some possible choices:

- Prince Gabriel of Belgium
- Christian, Crown Prince of Denmark
- Prince Hashem of Jordan
- Prince Lerotholi Seeiso of Lesotho
- Prince Georg of Liechtenstein
- Prince Nikolaus of Liechtenstein
- Prince Alfons of Liechtenstein
- Moulay Hassan, Crown Prince of Morocco
- Prince Paul-Louis of Nassau
- Prince Léopold of Nassau
- Prince Jean of Nassau
- Prince Sverre Magnus of Norway

Not royal but would still give her a title:

- Count Nikolai of Monpezat
- Count Felix of Monpezat (both have a small amount of Asian ancestry through their mother if that’s important to Aiko)
- Count Claus-Casimir of Orange-Nassau
- James, Earl of Wessex

Untitled but royal-adjacent:

- All grandsons of Juan Carlos I
- Arthur Chatto

She also has many non-reigning (and other reigning) possibilities. However Japan could always just update their sexist rules (and make the spouses of princesses princes/princesses instead).

 

[Mbruno]

If Aiko wants to remain royal after she marries she can marry a prince from another country (surprised that no Japanese princesses have done so). Here are some possible choices:

- Prince Gabriel of Belgium
- Christian, Crown Prince of Denmark
- Prince Hashem of Jordan
- Prince Lerotholi Seeiso of Lesotho
- Prince Georg of Liechtenstein
- Prince Nikolaus of Liechtenstein
- Prince Alfons of Liechtenstein
- Moulay Hassan, Crown Prince of Morocco
- Prince Paul-Louis of Nassau
- Prince Léopold of Nassau
- Prince Jean of Nassau
- Prince Sverre Magnus of Norway

Not royal but would still give her a title:

- Count Nikolai of Monpezat
- Count Felix of Monpezat (both have a small amount of Asian ancestry through their mother if that’s important to Aiko)
- Count Claus-Casimir of Orange-Nassau
- James, Earl of Wessex

Untitled but royal-adjacent:

- All grandsons of Juan Carlos I
- Arthur Chatto

She also has many non-reigning (and other reigning) possibilities. However Japan could always just update their sexist rules (and make the spouses of princesses princes/princesses instead).

Guess he can marry Leonor then, wonder what would happen if that were to occur. The idea of a Japanese king/prince consort of Spain is quite interesting (that seems more likely than Japan accepting a foreign empress). Or maybe they would actually be allowed to be monarchs of their own countries and consorts of each other’s (oldest son would succeed to the Japanese throne and the oldest other child would succeed to the Spanish one).

Marrying a non-Christian would be in practice not acceptable in my view for a senior royal in Denmark or the UK, which have established Protestant churches, and probably also unlikely in Spain or Belgium, which do not have established churches, but where the Royal Family is in practice closely associated with the Roman Catholic Church.

For sure it is not a strict legal requirement, but, in practice, Mary Donaldson, who was already a Christian, but a Presbyterian, joined the Lutheran Church of Denmark when she married CP Frederik, and so did Prince Henrik, formerly a Catholic, when she married the future Queen Margrethe. And, in the UK, Meghan Markle had to be baptized in the Church of England before marrying Prince Harry. Apparently Meghan had not been baptized before, so I think it is safe to assume she was not a Christian prior to her wedding, even though she attended a Catholic school as a child.

In Spain, on the other, Sophia of Greece, who was an Orthodox Christian, joined the Roman Catholic Church to marry Prince (future King) Juan Carlos, as did Princess Victoria Eugenie of Battenberg, formerly an Anglican Christian, to marry King Alfonso XIII. Both of the aforementioned marriages, however, took place before the disestablishment of the Roman Catholic Church in Spain in 1978, so it is unclear what would happen if Leonor decided to marry a non-Christian.

Also the succession is governed by law or the constitution, depending on the country. In Spain, for example, it would be impossible " for the oldest son to succeed to the Japanese throne and the oldest other child to succeed to the Spanish one" because the oldest son would be legally the heir to the Spanish throne, The only alternative to circumvent that would be if the oldest son renounced his succession rights in Spain, which would require an organic act passed by the Spanish Parliament under Article 57 (5) of the Spanish constitution:

Article 57 [Succession]
(1) The Crown of Spain is hereditary for the successors of H.M. Don Juan Carlos I of Borbon, legitimate heir of the historic dynasty. Succession to the throne will follow the regular order of primogeniture and representation, the first line always having preference over subsequent lines; within the same line, the closer grade over the more remote; in the same grade, the male over the female; and in the same sex, the elder over the younger.
(2) The hereditary Prince, from his birth or from the time he acquires the claim, will have the title of Prince of Asturias and the other titles traditionally linked to the successor to the Crown of Spain.
(3) If all the lines entitled by law become extinct, the Parliament shall provide for the succession to the crown in the manner which is best for the interests of Spain.
(4) Those persons, who having the right to succession to the throne, contract matrimony against the express prohibition by the King and the Parliament, shall be excluded, along with their descendants, from succession to the Crown.
(5) Abdications and renunciations and any doubt in fact or in law which may occur in the order of succession to the Crown, shall be resolved by an organic law.

It would not make sense either for the oldest son to renounce his succession rights until he came of age. In fact, I am not sure if a minor can legally make a renunciation.

 

[Biri]

If Aiko wants to remain royal after she marries she can marry a prince from another country (surprised that no Japanese princesses have done so). Here are some possible choices:

- Prince Gabriel of Belgium
- Christian, Crown Prince of Denmark
- Prince Hashem of Jordan
- Prince Lerotholi Seeiso of Lesotho
- Prince Georg of Liechtenstein
- Prince Nikolaus of Liechtenstein
- Prince Alfons of Liechtenstein
- Moulay Hassan, Crown Prince of Morocco
- Prince Paul-Louis of Nassau
- Prince Léopold of Nassau
- Prince Jean of Nassau
- Prince Sverre Magnus of Norway

Not royal but would still give her a title:

- Count Nikolai of Monpezat
- Count Felix of Monpezat (both have a small amount of Asian ancestry through their mother if that’s important to Aiko)
- Count Claus-Casimir of Orange-Nassau
- James, Earl of Wessex

Untitled but royal-adjacent:

- All grandsons of Juan Carlos I
- Arthur Chatto

She also has many non-reigning (and other reigning) possibilities. However Japan could always just update their sexist rules (and make the spouses of princesses princes/princesses instead).

She would have to convert from Shinto to Christianiy then.

 

[meeralakshmi]

Marrying a non-Christian would be in practice not acceptable in my view for a senior royal in Denmark or the UK, which have established Protestant churches, and probably also unlikely in Spain or Belgium, which do not have established churches, but where the Royal Family is in practice closely associated with the Roman Catholic Church.

For sure it is not a strict legal requirement, but, in practice, Mary Donaldson, who was already a Christian, but a Presbyterian, joined the Lutheran Church of Denmark when she married CP Frederik, and so did Prince Henrik, formerly a Catholic, when she married the future Queen Margrethe. And, in the UK, Meghan Markle had to be baptized in the Church of England before marrying Prince Harry. Apparently Meghan had not been baptized before, so I think it is safe to assume she was not a Christian prior to her wedding, even though she attended a Catholic school as a child.

In Spain, on the other, Sophia of Greece, who was an Orthodox Christian, joined the Roman Catholic Church to marry Prince (future King) Juan Carlos, as did Princess Victoria Eugenie of Battenberg, formerly an Anglican Christian, to marry King Alfonso XIII. Both of the aforementioned marriages, however, took place before the disestablishment of the Roman Catholic Church in Spain in 1978, so it is unclear what would happen if Leonor decided to marry a non-Christian.

Also the succession is governed by law or the constitution, depending on the country. In Spain, for example, it would be impossible " for the oldest son to succeed to the Japanese throne and the oldest other child to succeed to the Spanish one" because the oldest son would be legally the heir to the Spanish throne, The only alternative to circumvent that would be if the oldest son renounced his succession rights in Spain, which would require an organic act passed by the Spanish Parliament under Article 57 (5) of the Spanish constitution:




It would not make sense either for the oldest son to renounce his succession rights until he came of age. In fact, I am not sure if a minor can legally make a renunciation.

If Aiko were to marry a minor European royal (like any of Prince Guillaume’s sons) would she be expected to convert? If she were to marry a Muslim prince she would have to convert to Islam though I’m not sure if the dowager crown princess of Bulgaria did when she married Prince Ghazi of Jordan. I guess if Hisahito were to marry Leonor he would give up his Japanese succession rights and become Spain’s consort. He would convert to Catholicism of course.

She would have to convert from Shinto to Christianiy then.

Or Islam if she married a Muslim prince. However idk if she would have to convert if she married a minor royal.

 

[Biri]

If Aiko were to marry a minor European royal (like any of Prince Guillaume’s sons) would she be expected to convert? If she were to marry a Muslim prince she would have to convert to Islam though I’m not sure if the dowager crown princess of Bulgaria did when she married Prince Ghazi of Jordan. I guess if Hisahito were to marry Leonor he would give up his Japanese succession rights and become Spain’s consort. He would convert to Catholicism of course.

No,she didn't - she remained a Christian, but Christians are considered to be the People of the Book in Islam.
When a Muslim man marries a woman from the People of the Book, she may retain her faith (however, their eventual children must be raised as Muslims; but Miriam was in already post-childbearing age while marrying Ghazi).

 

[Stefan]

I guess if Hisahito were to marry Leonor he would give up his Japanese succession rights and become Spain’s consort. He would convert to Catholicism of course.

I don't think the IHA would ever allow Hisahito to give up his succession rights, and it would be rather Leonor who would have to give up her succession rights.
But i think they would never allow such a marriage and do everything to prevent it.

For sure it is not a strict legal requirement, but, in practice, Mary Donaldson, who was already a Christian, but a Presbyterian, joined the Lutheran Church of Denmark when she married CP Frederik, and so did Prince Henrik, formerly a Catholic, when she married the future Queen Margrethe. And, in the UK, Meghan Markle had to be baptized in the Church of England before marrying Prince Harry. Apparently Meghan had not been baptized before, so I think it is safe to assume she was not a Christian prior to her wedding, even though she attended a Catholic school as a child.

Also Alexandra and Marie converted before their marriages. Marie was of course catholic but if i rember rigth Alexandra belonged to the anglican Church and had to be confirmed again in the danish-lutheran Church

 

[meeralakshmi]

If there are any blue-eyed princesses born circa 2006, then one of them for future emperor Hisahito of Japan, in the hopes that Hiranuma Takeo (the politician who stated prior to Hisahito's birth that "If Aiko becomes the reigning empress, and gets involved with a blue-eyed foreigner while studying abroad and marries him, their child may be the emperor. We should never let that happen") will be asked to comment.

Princess Isabella of Denmark is a blue-eyed princess who would be a less complicated choice than Leonor not being an heir.

 

[Biri]

Would eventual European Princess-the wife of future Emperor Hisahito be allowed to remain a Christian?

 

[meeralakshmi]

Would eventual European Princess-the wife of future Emperor Hisahito be allowed to remain a Christian?

Not sure, either she would have to convert or there would be an agreement that their kids be raised Shinto (or their sons would be raised Shinto and their daughters Lutheran).

Though she may need to convert to Catholicism a non-reigning option for Aiko would be a Brazilian prince since there are a lot of Japanese Brazilians.

 

[Tatiana Maria]

Would eventual European Princess-the wife of future Emperor Hisahito be allowed to remain a Christian?

The present emperor's late cousin Prince Tomohito of Mikasa married a member of a prominent political family which happens to be Christian. I have never heard that she was required to renounce her Christianity upon marrying into the imperial family, though perhaps @Prisma or @MarieAmelie_95 will know more. There was a post not too long ago about one of her daughters being seen privately visiting a church.

Religion is largely viewed in Japan as a personal matter (one exception is that certain Shinto rites are treated as belonging to the imperial family's duties for historical reasons). When Princess Tomohito (Nobuko)'s brother Aso Taro became prime minister, Western media reports frequently mentioned that he was Japan's first Catholic prime minister; however, very few people in Japan even knew, or would have cared, that he was Christian.

She would have to convert from Shinto to Christianiy then.

From a Japanese perspective, there is no issue with practicing both Shinto and Christianity. There exists a Japanese aphorism: "born Shinto, marry Christian, die Buddhist", referring to the rituals held to commemorate these life events.

I don't think the IHA would ever allow Hisahito to give up his succession rights, and it would be rather Leonor who would have to give up her succession rights.
But i think they would never allow such a marriage and do everything to prevent it.

Neither Prince Hisahito nor the Imperial Household Agency enjoys control over his rights to the Japanese throne, as the succession to the throne is regulated by Act of Parliament - currently, the Imperial House Law of 1947, which does not permit renunciations (thus, Emperor Akihito's abdication needed to be authorized by another Act of Parliament). The Diet (Parliament) is the only entity empowered to remove Hisahito's succession rights.

Marrying a non-Christian would be in practice not acceptable in my view for a senior royal in Denmark or the UK, which have established Protestant churches, and probably also unlikely in Spain or Belgium, which do not have established churches, but where the Royal Family is in practice closely associated with the Roman Catholic Church.

For sure it is not a strict legal requirement, but, in practice, Mary Donaldson, who was already a Christian, but a Presbyterian, joined the Lutheran Church of Denmark when she married CP Frederik, and so did Prince Henrik, formerly a Catholic, when she married the future Queen Margrethe. And, in the UK, Meghan Markle had to be baptized in the Church of England before marrying Prince Harry. Apparently Meghan had not been baptized before, so I think it is safe to assume she was not a Christian prior to her wedding, even though she attended a Catholic school as a child.

In Spain, on the other, Sophia of Greece, who was an Orthodox Christian, joined the Roman Catholic Church to marry Prince (future King) Juan Carlos, as did Princess Victoria Eugenie of Battenberg, formerly an Anglican Christian, to marry King Alfonso XIII. Both of the aforementioned marriages, however, took place before the disestablishment of the Roman Catholic Church in Spain in 1978, so it is unclear what would happen if Leonor decided to marry a non-Christian.

Meghan Markle identified as a Protestant Christian, as the UK royal court described her as "a Protestant" to reporters at the time of the engagement, before her Anglican baptism. I imagine many not particularly devout Christians might not bother with a baptism ceremony. Another possibility is that she had a prior baptism using a rite not recognized as valid by the Church of England. An article at the time noted that some American churches conducted their baptisms "in the name of Jesus Christ" rather than the Anglican baptismal formula of "in the name of the Father, the Son, and the Holy Ghost" and that the former would not be recognized by the Church of England.

I concur with you that older generations of European consorts often experienced strong expectations to join the official or unofficial national church of the country they married into (especially in the case of Sofia of Greece, whose husband needed to remain acceptable to the devoutly Catholic Francisco Franco). But the more recent changes from one Christian church to another may be more reflective of the declining religiosity in Europe and other historically Christian regions. If a Christian consort is not really devout (and Henrik, Mary and Meghan did not seem to be), they are unlikely to care about the differences between Protestant, Catholic and Orthodox Christianity, and even less likely to care about the minor distinctions between different Protestant churches. If all Christian churches are equally acceptable as far as they are concerned, they might as well join the one associated with the royal family they married into.