Joan of Habsburg

Joan, Infanta of Spain (Sp. 'Juana'), of the Habsburg family, daughter of Emperor Charles V who was the first king of united Spain (officially King of Aragon and king of Castile), and his consort Infanta Isabel of Portugal, daughter of King Manuel I of Portugal.

As such, Juana was an Archduchess of Austria, Infanta of Castile and of Aragon, Princess of Burgundy and Flanders, daughter of Roman Emperor, etc.

She married her first cousin, Infante Joao of Portugal, who was the heir of Portugal, the sole surviving son of her paternal aunt Catherine of Habsburg and her maternal uncle King John of Portugal. Their teenage marriage led to pregnancy (Joao was 15 y.o. when his wife conceived), and their only child Sebastian of Portugal was born posthumously in 1554 a couple of weeks after the teenager father Joao had perished in tuberculosis at the age of 16 years.