The only child of Enrique IV of Castile and Juana of Portugal, Juana’s legitimacy was contested right from the beginning, due to her father’s supposed impotency. The popular belief that she was fathered by the king’s favourite, Beltran de la Cueva, gave her the nickname of La Beltraneja. Another theory is that Juana was conceived by the earliest known form of in vitro fertilization, as was recorded by a german traveler. Her mother’s scandalous affair with Pedro of Castile and the birth of two illegitimate sons further damaged Juana’s position.
In 1464, in conflict with the powerful castilian nobility, Enrique declared his half-brother Alfonso his heir and betrothed Alfonso and the infant Juana, which fell through when Alfonso was crowned by the nobility of the Levante. Juana was then suggested as bride for the future João II of Portugal. Raised in the household of the Mendozas, she was once again deprived of her position by the Treaties of Guisando, where her aunt Isabel was declared heir, which was broken shortly afterwards. In 1470, she was married by proxy to the Duke of Guyenne, who died suddenly.
Enrique IV’s death in 1474 sparked a conflict between Juana and Isabel. Juana’s uncle, Afonso V of Portugal presented himself as her champion, whom he married by proxy as Juana was still in the custody of the Marquis of Villena, and later in person in the city of Segovia. The groom was forty-two years old and the bride was twelve. The marriage was unconsummated both due to her young age and because of the lack of necessary a papal bull due to the consanguinity between the spouses. The portuguese invasion of Castile, which Juana accompanied by her husband’s side, was a military disaster and Afonso V was defeated in the Battle of Toro and retreated to Portugal. Juana was in an uncomfortable position and the court was unwilling to recognize her as Queen Consort.
Her marriage was annulled, the Treaty of Alcáçovas declared her illegitimate and Portugal abandoned its defense of her claim. She was given the option of marrying her infant cousin Juan (having to wait 13 years until the groom came of age) or to take vows as a nun, of which she chose the later, being recorded as being reluctant and revolted on the day of her vows. Afonso V died shortly afterwards, determining in his will that Juana should enjoy the dignity and honors of a infanta of Portugal. She left the convent in the same year and enjoyed the use of her own court provided by the Portuguese Crown, being visited often by João II and his successor Manuel I, who referred to her as his “most beloved and prized cousin”.
Juana outlived all of her rivals, dying at the age of 68. She signed Yo la Reina (I the Queen) during her entire life, and was the first to enjoy the title of Excellency in the Portuguese language, being known as The Excellent Lady. Her tomb in the Monastery of Santa Clara in Lisbon disappeared in the 1755 earthquake.