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Portuguese royalty
House of Aviz

John I Children    Infante Duarte (future Edward I)    Infante Pedro, Duke of Coimbra    Henry the Navigator (Infante Henrique, Duke of Viseu)    Infanta Isabel, Duchess of Burgundy    Infante João    Infante Fernando, the Saint Prince    Afonso, Duke of Braganza (illegitimate)    Beatriz, Countess of Arundel (illegitimate) Grandchildren include    Infanta Isabel of Coimbra, Queen of Portugal Edward Children    Afonso, Prince of Portugal (future Afonso V)    Infante Fernando, Duke of Viseu    Infanta Leonor, Holy Roman Empress    Infanta Catarina    Infanta Joana, Queen of Castile Grandchildren include    Infante Manuel, Duke of Beja (future Manuel I)    Infanta Leonor of Viseu, Queen of Portugal Afonso V Children include    João, Prince of Portugal    Blessed Joana, Princess of Portugal    João, Prince of Portugal (future John II) John II    Afonso, Prince of Portugal    Jorge, Duke of Coimbra (illegitimate) Manuel I Children include    Miguel da Paz, Prince of Portugal and of Asturias    João, Prince of Portugal (future John III)    Infanta Isabel, Holy Roman Empress    Infanta Beatriz, Duchess of Savoy    Infante Luís, Duke of Beja    Infante Fernando, Duke of Guarda and Trancoso    Infante Cardinal Afonso    Infante Cardinal Henrique (future Henry I)    Infante Duarte, Duke of Guimarães    Infanta Maria Grandchildren include    Philip II of Spain (future Philip I of Portugal)    António, Prior of Crato (future Anthony I) (illegitimate)    Infanta Maria of Guimarães, Duchess of Parma and Piacenza    Infanta Catarina of Guimarães, Duchess of Braganza Great-Grandchildren include    Teodósio II, Duke of Braganza    Rannuccio Farnense of Parma Great-Great-Grandchildren include    John II, Duke of Braganza (future John IV of Portugal) John III Children include    Maria Manuela, Princess of Portugal and of Asturias    João, Prince of Portugal Grandchildren include    Sebastião, Prince of Portugal (future Sebastian I)    Carlos, Prince of Asturias Sebastian Henry Anthony (disputed king)

Prince Afonso of Portugal (Portuguese pron. IPA [ɐ'fõsu]; English: Alphonzo) (May 18, 1475 – July 13, 1491), was the heir to the throne of Portugal. He was born in in Lisbon, Portugal, and died in a horse riding accident in the margins of the Tagus river.

Alfonso was the only son and heir of king John II of Portugal by his marriage with Leonor of Viseu, princess of Portugal. The king was very fond of him and named the smaller island of São Tomé and Príncipe after him (Príncipe meaning Prince in Portuguese language).

As a boy, Alfonso was married to Isabella of Aragon, the eldest daughter of the catholic royal couple, reyes catolicos. Isabella I of Castile and Ferdinand II of Aragon had a male heir - Juan, Prince of Asturias - but he was a feeble child and not expected to survive. Princess Isabella was thus the probable heiress to the joint throne of Castile and Aragon and, by being married to the heir of Portugal that meant a union of the Iberian kingdoms in Portuguese hands. The Spanish monarchs apparently desired this not to happen. They tried every diplomatic channel to have the wedding dissolved, without success, due to Portuguese influence with the Pope. Their cause was apparently lost, when an accident saved Aragon and Castile from future annexation.

Alfonso died after falling off his horse under mysterious circumstances, during a ride in the Tagus. Murder was never proven but the Spanish had much to gain from his disappearance. Moreover, the prince's valet, an exiled Castilian boy, disappeared the same day after being the only eyewitness of the event.

With Alfonso's death, John II was left with no legitimate male heirs, and the crown then went to Manuel I of Portugal when John died in 1495. Afonso's widow Isabella was married to Manuel, thus again creating the possibility of a union of all Iberian kingdoms. Isabella bore a son, Miguel (born 1498 and died 1500). Manuel's chance to become the king-consort of Spain vanished on the death of Isabella in 1498. After the death of Juan, Prince of Asturias, baby Miguel of Portugal became heir to the Spanish crowns and was recognized as Prince of Asturias. His death in 1500 put a final end to the possibility of this union, and Joan the Mad (Miguel's aunt) became the heiress of Spain, eventually bringing those kingdoms to the Habsburgs. The union took place about a hundred years later, 1580, when the Habsburg king of Spain, Philip II, grandson of Joan the Mad and grandson of Manuel of Portugal, annexed Portugal and its dominions.