Beatrice (, ; 7–13 February 1373 – ) was the only surviving legitimate child of King Ferdinand I of Portugal and his wife, Leonor Teles. She became Queen consort of Castile by marriage to King John I of Castile. Following her father's death without a legitimate male heir, she claimed the Portuguese throne, but lost her claim to her uncle, who became King John I of Portugal, founder of the House of Aviz.
During her early years, Beatrice was a pawn in the changing politics of foreign alliances of her father, who negotiated successive marriages for her. She would eventually marry King John I of Castile, by whom Beatrice became Queen consort of Castile. At the death of her father, Beatrice was proclaimed Queen regnant of Portugal and her mother assumed the regency in her name. Opposition to the regency, fear of the Castilian domination and loss of Portuguese independence led to a popular rebellion and civil war between the late King Ferdinand I's illegitimate brother, John of Aviz, who wrested control of the regency from the dowager queen, and the supporters of Beatrice and her husband, John I of Castile, who claimed the throne of Portugal by right of his wife. In 1385, John of Aviz was proclaimed King of Portugal, and the King of Castile was definitively defeated in the Battle of Aljubarrota, effectively ending any prospects for Beatrice and her husband to assert their rights to the Portuguese crown.
From that time, Queen Beatrice took a special interest in the welfare of the Portuguese exiles in Castile who had been faithful to her dynastic claim to the Portuguese throne. After the death of her husband she was relegated to a secondary level in the Castilian court. However, the dynastic strife continued to represent a challenge to the normalization of relations between Castile and Portugal. From the second decade of the 15th century onwards, her documentary trail became scarce until she completely disappears about 1420.
Life
Early years and betrothals
Beatrice was born in Coimbra, during the brief siege of the city by Castilian troops during the second Fernandine War (1372–73). The siege was lifted and King Henry II of Castile continued to Santarém and then Lisbon. During the siege of Lisbon, Cardinal legate Guido of Bologna obtained an agreement between the Kings of Castile and Portugal, the Peace of Santarém. According to that treaty, King Ferdinand I of Portugal would abandon the 'Petrist' cause, his claim to dynastic legitimacy that originated after the assassination of King Peter I of Castile in 1369. Two marriages were celebrated between the two royal families to reinforce the peace: between Sancho Alfonso, 1st Count of Alburquerque, brother of Henry, and Beatrice, half-sister of Ferdinand, and between Alfonso Enríquez, Henry's natural son, and Ferdinand's illegitimate daughter Isabel. In addition, a betrothal was arranged between Beatrice, Ferdinand I of Portugal's newborn daughter, and Fadrique, created Duke of Benavente, another natural son of King Henry II of Castile.
The Cortes de Leiria of 1376 pledged to support Beatrice as heiress of the throne, accepting her betrothal with the Duke of Benavente. The betrothal was solemnized in Leiria on 24 November 1376, and on 3 January 1377 was accepted by King Henry II.
Fernando I's will of 1378 ratified all agreements concerning Beatrice, adding that in the absence of Beatrice or any descendants, the Portuguese king's half-brothers, the children of Inês de Castro (John, Diniz and Beatrice) were disinherited, and the throne of Portugal would passed to any hypothetical sisters of Beatrice, and after them, to Duke Fadrique of Benavente. To ensure the succession of the throne in her daughter, Queen Leonor Teles devised a plot against John of Portugal, in which the Queen's own sister María Teles, John's wife, was accused of adultery and killed by her husband in June 1379. Although John later obtained the royal pardon, he opted to flee to Castile, fearful of the Teles family.