Juana I of Castile

Joanna or Joan (also known as Joanna the Mad or Joan the Mad; Spanish: Juana la Loca; 6 November 1479 – 12 April 1555) was Queen of Castile from 1504 and Queen of Aragon from 1516 to her death in 1555. She was the daughter of Queen Isabella I of Castile and King Ferdinand II of Aragon. Joanna was married by arrangement to the Austrian archduke Philip the Handsome on 20 October 1496. Following the deaths of her elder brother John, elder sister Isabella, and nephew Miguel between 1497 and 1500, Joanna became the heir presumptive to the crowns of Castile and Aragon. When her mother died in 1504, she became queen of Castile. Her father proclaimed himself governor and administrator of Castile.

In 1506, Joanna's husband Philip became King of Castile jure uxoris as Philip I, initiating the rule of the Habsburgs in the Spanish kingdoms. Philip died that same year. Despite being the ruling Queen of Castile, Joanna had little effect on national policy during her reign as she was declared insane and confined in the Royal Palace in Tordesillas under the orders of her father, who ruled as regent until his death in 1516, when she inherited his kingdom as well. Her son Charles I became king, and during his reign, Joanna was nominally co-monarch but remained confined until her death. She died aged 75 in 1555. Historians have debated the authenticity of her alleged madness, and whether or not it was used to discredit her.