John, Prince of Asturias, only son of Ferdinand II of Aragon and Isabella I of Castile (born 1478)

John, Prince of Asturias and Girona was the only son of King Ferdinand II of Aragon and Queen Isabella I of Castile, and heir apparent to both their thrones for nearly his entire life.

Ferdinand II, also known as Ferdinand I, Ferdinand III, and Ferdinand V, called Ferdinand the Catholic, was King of Aragon from 1479 until his death in 1516. As the husband and co-ruler of Queen Isabella I of Castile, he was also King of Castile from 1475 to 1504. He reigned jointly with Isabella over a dynastically unified Spain; together they are known as the Catholic Monarchs. Ferdinand is considered the de facto first king of Spain, and was described as such during his reign, even though, legally, Castile and Aragon remained two separate kingdoms until they were formally united by the Nueva Planta decrees issued between 1707 and 1716.

Isabella I, also called Isabella the Catholic, was Queen of Castile and León from 1474 until her death in 1504. She was also Queen of Aragon from 1479 until her death as the wife of King Ferdinand II. Reigning together over a dynastically unified Spain, Isabella and Ferdinand are known as the Catholic Monarchs. Her reign marked the end of Reconquista and also the start of Spanish Empire and dominance of Spain over European Politics for the next century.