The Crown of Castile[nb 1] was a medieval state in the Iberian Peninsula that formed in 1230 as a result of the third and definitive union of the crowns and, some decades later, the parliaments of the kingdoms of Castile and León upon the accession of the then Castilian king, Ferdinand III, to the vacant Leonese throne. It continued to exist as a separate entity after the personal union in 1469 of the crowns of Castile and Aragon with the marriage of the Catholic Monarchs up to the dynastic union occasioned by the succession of Charles I of Spain, the Habsburg heir to both crowns in 1516.
More information on the Wikipedia page [1].