The Infante John, Prince of Asturias, (30 June 1478 – 4 October 1497) was the only son of Queen Isabella I of Castile and King Ferdinand II of Aragon who survived to adulthood. The name is an anglicization of the Spanish Juan, a name shared by his half-brother John, Prince of Girona, as well as many other Don Juans.
John was born in Seville in 1478 to the sovereigns of Castile, Isabella I and Ferdinand V. At the time, his parents were involved in the War of Castilian Succession against Isabella's niece Joanna la Beltraneja, wife of King Afonso V of Portugal.
John's birth helped consolidate Isabella's position as sovereign as she had given birth to a legitimate male heir. At the time of his birth, he had one elder sister Isabella; he was joined by Joanna, Maria and Catherine.
His parents won the war against the King and Queen of Portugal. To negotiate a peace settlement with Isabella, Alfonso sent Infanta Beatrice, Duchess of Viseu. The two women met in March 1479. Beatrice was Afonso's sister-in-law and Isabella’s maternal aunt.