| Diego | |
| Full Name: | Diego Felix |
| Prince of Asturias and Portugal | |
| House: | Habsburg |
| Father: | Philip II of Spain |
| Mother: | Anna of Austria |
| Birth Date: | 15 August 1575 |
| Birth Place: | Madrid, Crown of Castile, Spain |
| Death Place: | Madrid, Crown of Castile, Spain |
| Burial Place: | El Escorial |
Diego, Prince of Asturias and Portugal (Diego Felix; 15 August 1575 - 21 November 1582) was the fourth son of Philip II of Spain and his third son by his fourth wife, Anna of Austria.
At the time of his birth, Diego's elder brother, Prince Ferdinand, was still the heir-apparent. On the death of Ferdinand in 1578, Diego became heir-apparent to the throne. Diego also had another elder brother, Carlos Lorenzo, who died in infancy. His mother had just learned of the death of Carlos Lorenzo, and she was said to have suffered such a shock from word of his death that it caused her to go into premature labour, giving birth to Diego.He was formally invested as Prince of Asturias on 1 March 1580 by the Courts in Madrid.[1] The poet Cristóbal de Virués dedicated a sonnet to the new Prince, where he proposed that Diego follow the steps of his father.[2]
In 1580, his father became king of Portugal as well, making Diego heir-apparent of that realm also. His mother, Anna, died during a trip to their new kingdom. Diego and his siblings remained in Madrid under the care of their half-sisters Isabella Clara Eugenia and Catherine Michelle. The letters of Philip II make clear that he was extremely proud of Diego: he wrote that his son had already learned the alphabet and dancing by the age of five. In a letter dated 1582 the king wrote to the Indian Viceroy Francisco de Mascarenhas commanding that he bring an elephant to the Prince of Asturias as a gift. Philip II taught his son the Portuguese language so that one day Diego could speak as king with his Portuguese subjects. In addition, Philip II planned to betroth Diego to one of the daughters of John, Duke of Braganza and Catherine of Portugal, thus strengthening his claim to the Portuguese throne.
Diego never became king. In late 1582 he contracted smallpox and died at the age of 7. At his death, Philip II was inconsolable, for the only heir-apparent to the throne remaining was the small and sickly Infante Philip, who assumed the position of Prince of Asturias. The King gave orders that continuous prayers be said at the Church of Our Blessed Lady in Zaragoza for the health of the royal children remaining.
Diego's younger brother became King Philip III upon their father's death in 1598.