 Ferdinand was born in Sada Palace, Sos del Rey Católico, Kingdom of Aragon, as the son of John II of Aragon (whose family was a cadet branch of the House of Trastámara) by his second wife, Juana Enríquez.He married Infanta Isabella, the half-sister and heiress of Henry IV of Castile, on 19 October 1469 in Valladolid, Kingdom of Castile and Leon.Isabella also belonged to the royal House of Trastámara, and the two were cousins by descent from John I of Castile.