Joanna of Austria, Princess of Portugal

Joanna of Austria (in Castilian, Doña Juana de Austria; in Portuguese, Dona Joana de Áustria, 24 June 1535 – 7 September 1573) was Princess of Portugal by marriage to João Manuel, Prince of Portugal. She served as regent of Spain to her brother Philip II during his trips to England to marry Mary I from 1554 to 1556, and 1556 to 1559. She was the mother of King Sebastian of Portugal.

Married at 16 to her even younger husband, she was widowed after two years, giving birth in the same month. Later that year she returned to Spain at her father's request, leaving her son in the care of her mother-in-law, who was also her aunt. She never saw him again, but corresponded and had portraits sent. In later life she was active in religious affairs.