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Born in Castile, Fernando of Aragon was the son of King Juan II of Aragon and Juana Enríquez. He became the King of Sicily in 1468 and later the King of Aragon in 1479. His marriage to Queen Isabella I of Castile in 1469 united the two kingdoms under one crown, marking the beginning of the unification of modern-day Spain, though both kingdoms maintained their own political autonomy.