Queen Juana of Castile (1479-1555) was the daughter of Ferdinand of Aragon and Isabella of Castile and a sister of Katherine of Aragon. Known as "Juana la Loca" ("Jane the Mad"), her mental health was often strained by her unrequited love for her unfaithful husband, Philip I of Castile, and by the control of her male relatives over her. Juana may well have been bipolar rather than truly mad.