John II (Catalan: Joan II, Aragonese: Chuan II and Basque: Joanes II), called the Great (el Gran) or the Faithless (el Sense Fe) (29 June 1398 – 20 January 1479), was the King of Navarre through his wife (jure uxoris) from 1425 and the King of Aragon in his own right from 1458 until his death. He was the son of Ferdinand I and his wife Eleanor of Alburquerque.

John was born at Medina del Campo (in the Crown of Castile). In his youth he was one of the infantes (princes) of Aragon who took part in the dissensions of Castile during the minority and reign of John II. Till middle life he was also lieutenant-general in Aragon for his brother and predecessor Alfonso V, whose reign was mainly spent in Italy. In his old age he was engaged in incessant conflicts with his Aragonese and Catalan subjects, with Louis XI of France, and in preparing the way for the marriage of his son Ferdinand with Isabella I of Castile which brought about the union of the crowns of Aragon and Castile and which was to create the Kingdom of Spain. His troubles with his subjects were closely connected with tragic dissensions within his own family.

John was first married to Blanche I of Navarre of the house of Évreux. By right of Blanche he became king of Navarre, and on her death in 1441 he was left in possession of the kingdom for his lifetime. But one son, Charles, given the title "Prince of Viana" as heir of Navarre, had been born of the marriage. John quickly came to regard this son with jealousy. After his second marriage, to Juana Enríquez, it grew into absolute hatred, being encouraged by Juana. John tried to deprive his son of his constitutional right to act as lieutenant-general of Aragon during his father's absence. Charles's cause was taken up by the Aragonese, however, and the king's attempt to make his second wife lieutenant-general was set aside.

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