I know that but why it is not that the Heir is HRH Infanta Sofia of Spain, Princess of Asturias like it is in other monarchies. So the Heir would be a Prince/Princess but still of Spain
It is simply that different monarchies have different traditions. Likewise,
the Crown Princess of Sweden does not carry an extra title of Princess of Sweden.
In the Spanish monarchies, as Mbruno said, King/Queen and Prince/Princess have always superseded the lesser title of Infante/Infanta from the moment the holder became entitled to the higher title. The full titles of King Carlos IV of Spain are
given in a legal text quoted on the official website of Casa Real as:
Sirva como muestra la extensa titulación de Carlos IV, todavía en 1805, plasmada en la Real Cédula que precedía al texto legal de la Novísima Recopilación de las Leyes de España con ocasión de su promulgación: “Don Carlos por la gracia de Dios, Rey de Castilla, de León, de Aragón, de las Dos Sicilias, de Jerusalem, de Navarra, de Granada, de Toledo, de Valencia, de Galicia, de Mallorca, de Menorca, de Sevilla, de Cerdeña, de Córdoba, de Córcega, de Murcia, de Jaén, de los Algarbes, de Algeciras, de Gibraltar, de las Islas de Canaria, de las Indias Orientales y Occidentales, islas y Tierra firme del mar Océano; Archiduque de Austria; Duque de Borgoña, de Brabante y de Milán; Conde de Apsburg, de Flandes, Tirol y Barcelona; Señor de Vizcaya y de Molina”.
Infante is absent from the list, in accordance with the Spanish rules.
But after he succeeded his fatehr as head of the Royal House he was never a Prince nor a King. The Royal Decree does not mention that a Count of Barcelona is no Infante. And he was also often to referred as Infate. So why not also his wife.
Count of Barcelona is one of the many titles of the Kings of Spain (see the list above). The family recognized him as king of Spain despite Spain's republican government, just as Constantine of Greece and Margareta of Romania are recognized by their families as king of Greece and queen of Romania respectively, disregarding that Greece and Romania are republics.
Do you have an example of when he was referred to as Infante after becoming the heir to the headship of the house? He was of course an Infante prior to that.
Juan Carlos for example was never Prince of Asturias although Franco at one point made him a “ Prince of Spain”, which is not a traditional Spanish royal title.
I believe Prince of Spain was used under the House of Austria, the dynasty which reigned over Spain prior to the Bourbons.
Felipe was styled His Royal Highness The Infante Felipe of Spain up until 1977 when the title of Prince of Asturias was conferred on him
He was entitled to be styled Prince as the heir apparent to the throne from 1975, and then became Prince of Asturias, as you pointed out, in 1977.
