He was the son of John Manuel, Prince of Portugal, and his wife, Joanna of Austria. Sebastian succeeded to the throne at the age of three, on the death of King John III, his paternal grandfather. Soon after his birth, his mother Joanna of Spain left her infant son to serve as Regent of Spain for her father, Emperor Charles V. After his abdication in 1556, she served in the same capacity for her brother Philip II of Spain. Joanna remained in Spain until her death in 1573, never to see her son again. Since Sebastian was still a child, the regency was handled first by his paternal grandmother, Catherine of Austria, and then by his great-uncle, Cardinal Henry of Évora. During this period Portugal continued colonial expansion in Angola, Mozambique, and Malacca, as well as the annexation of Macau in 1557.