'Queen' D.ª Beatriz of Portugal (& Castile) and her claim

[Marengo]

Beatriz I, Queen of Portugal and the Algarves, Queen of Castille and Leon (Coimbra 9 December 1392 -Madrigal, 8 March 1408 ); married in Elvas on 17 May, 1383 King Juan I of Castille (Zaragosa, 24 August 1358 -Alcalá de Henares, 9 October 1390)

Reign: 1383 - 1385 (de jure)

Predecessor: King Fernando I of Portugal and the Algarves

Succeeded by: King João I of Portugal and the Algarves

Child: Prince Miguel of Castille

Parents Beatriz: King Fernando I of Portugal and Dona Leonor Teles de Meneses

Parents Juan: King Enrique II of Castille and Princess Juana Manuel of Penafiel (Castille)

Siblings Beatriz: None

Siblings Juan: Queen Leonor of Navarra and Princess Juana of Castille

[Marengo]

Beatrice, in Portuguese Beatriz (pron. IPA: [biɐ'tɾiʃ]), (9 December 1372, Coimbra – 8 March 1408) was the only daughter of King Fernando I of Portugal and his wife, the Castilian Leonor Telles de Menezes. She married King Juan I of Castile and claimed to be Queen of Portugal in the 1383-1385 Crisis that ended with her uncle João I of Portugal being acclaimed King of Portugal.
At the beginning of 1383, the political situation in Portugal was not peaceful. Beatrice was the King's only child, and heir to the throne, after her younger brothers' deaths in 1380 and 1382. Her marriage was the political issue of the day and inside the palace, factions lobbied constantly. Ferdinand arranged and cancelled his daughter's wedding several times before settling for his wife's first choice, King Juan I of Castile. Juan had lost his wife, Infanta Leonor of Aragon the year before, and was happy to take the Portuguese heiress. The wedding took place on May 17, 1383 in the Portuguese city of Elvas. Beatrice was only eleven years old.
King Ferdinand died shortly thereafter, on October 22, 1383. According to the treaty between Castile and Portugal, the Queen Mother, Leonor Telles de Menezes, became regent in the name of her daughter and son-in-law. But not everybody in Portugal was happy about this state of affairs. The loss of independence was unthinkable for the majority of Portuguese freemen. A rebellion led by the Master of the Order of Aviz, the future João I, began in that year, leading to the 1383-1385 Crisis.

Read the entire wikipedia article here.

[Marengo]

John I (August 24, 1358 – October 9, 1390) (in Spanish: Juan I) was the king of Castile, was the son of Henry II and of his wife Juana Manuel of Castile, daughter of Juan Manuel, Duke of Penafiel, head of a younger branch of the royal house of Castile.
His first marriage, with Eleanor of Aragon on June 18th, 1375, produced most of his issue, including the future Kings Henry III of Castile and Ferdinand I of Aragon.
He ransomed Leon VI of Armenia from the Mamluks and out of pity granted him the lifetime lordship of Madrid, Villa Real and Andújar in 1383.
He had engaged in hostilities with Portugal. His first quarrel with Portugal was settled by his marriage, in 1382, with Beatrice of Portugal, daughter of King Ferdinand I of Portugal. On the death of his father-in-law in 1383, John endeavoured to enforce the claims of his wife, Ferdinand's only child, to the crown of Portugal. The 1383-1385 Crisis, a period of civil unrest and anarchy in Portugal, followed. He was resisted by the national sentiment of the Portuguese people, and was utterly defeated at the battle of Aljubarrota, on August 14, 1385.

Read the entire article here.

[Marengo]

The claim to the Portuguese throne of Beatriz resulted in a war between Portugal and Castille, read more about it:

The 1383–1385 crisis was a period of civil war in Portuguese history that began with the death of King Fernando I of Portugal, who left no male heirs, and ended with the accession to the throne of King João I in 1385, in the wake of the Battle of Aljubarrota.
In Portugal, this period is also known as the "Portuguese Interregnum", since it is a period when no crowned king reigned.

In 1383, King Fernando I of Portugal was dying. From his marriage with Leonor Telles de Menezes only a girl, princess Beatrice of Portugal, survived. Her marriage was the major political issue of the day, since it would determine the future of the kingdom.
Several political factions lobbied for possible husbands, which included English and French princes. Finally, the king settled for his wife's first choice, King Juan I of Castile. The marriage was celebrated in May 1383, but was not a widely accepted solution. This dynastic union meant that Portugal would lose independence to Castile; many nobles were fiercely opposed to this possibility, but they were not united under a common pretender to the crown. The two candidates, both illegitimate half-brothers of Fernando, were:

• João, son of Pedro I of Portugal and Inês de Castro, at the time living in Castile
• João, Great Master of Aviz, another natural son of Peter I, very popular among the Portuguese middle class and traditional aristocracy

On October 22, King Fernando died. According to the marriage contract, dowager queen Leonor assumed regency in the name of her daughter Beatrice and son-in-law, Juan I of Castile. Since diplomatic opposition was no longer possible, the party for independence took more drastic measures, starting the 1383–1385 crisis.

The first act of hostility was taken by the faction of João of Aviz in December 1383. John, the count of Andeiro and lover of the dowager queen, was murdered by a group of conspirators led by João of Aviz. Following this act of war, João was now the leader of the opposition. With the help of Nuno Álvares Pereira, a talented general, he took the cities of Lisbon, Beja, Portalegre, Estremoz and Évora. In retaliation, King Juan I of Castile entered Portugal and occupied the city of Santarém. In an effort to normalize the situation and secure his wife's crown, he forced queen Leonor to abdicate from the regency and took control of the country.

Read the entire wikipedia article here.