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 of Spain 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. Life Early years Born in Madrid, Joanna was the daughter of Charles V, Holy Roman Emperor, who was the first king of united Spain, officially King of Aragon and King of Castile and his wife, Isabella of Portugal. Therefore, her paternal grandparents were Philip of Castile and Joanna of Castile, and her maternal grandparents were Manuel I of Portugal and Maria of Aragon. She was the sister of King Philip II of Spain and Maria of Austria. Among others, Joanna held the titles of Archduchess of Austria, Infanta of Castile and of Aragon, and princess of Burgundy. Named for the saint's day of her birth (24 June is the Nativity of St. John the Baptist) and in honor of her paternal grandmother,queen Juana of Castile, Joanna of Austria was motherless at the age of four and was entrusted to Doña Leonor de Mascareñas. By age eight she could understand Latin and could play several musical instruments. Princess of Portugal On 11 January 1552, at the age of sixteen, she married her double first cousin, the fourteen-year-old crown prince of Portugal, John Manuel of Portugal, by proxy in Toro. She arrived at the Portuguese court in November 1552. The marriage was cut short when John Manuel died of tuberculosis at age sixteen on 2 January 1554. However, Joanna was pregnant by that time, and the future Portuguese king Sebastián I was born on 20 January 1554. Joanna returned to Spain in May 1554 at the request of her father, leaving her newborn son with her mother-in-law, the Portuguese Queen Catherine of