João Manuel, Prince of Portugal

The Infante João Manuel, Prince of Portugal (pronounced|ʒuˈɐ̃ũ mɐnuˈɛɫ; in English: "John Emannuel") (June 3, 1537 – January 2, 1554) was a Portuguese infante, the eighth son of King John III of Portugal by his wife Catherine of Habsburg (House of Habsburg), daughter of Philip of Burgundy and Joanna of Castile. As the heir to the throne he was styled Prince of Portugal.

João was born in June 3, 1537 in Évora and became the heir to the throne of Portugal in 1539. He survived his four older brothers who died in childhood but was a sickly teenager. The successive inter-marriages between the houses of Spain and Portugal probably had some responsibility for his ill health. In 1552 he married Joan of Spain (princess of Spain), his first cousin, through both paternal and maternal line, daughter of his paternal aunt Isabel of Portugal and of his maternal uncle Emperor Charles V.

João died of what the sources refer to as "consumption" (tuberculosis) on January 2, 1554, however it is worth mentioning that some historians believe his death occurred as a result of diabetes. Eighteen days later, a posthumous son was born from his marriage: the future King Sebastian I of Portugal. His death at the age of only 24 was the beginning of the succession problem in Portugal that would end in the loss of independence to Spain in 1580.