John was born at the Château d'Argentan, the son of John I of Alençon and Marie of Brittany. He first saw action at the age of fifteen at the Battle of Verneuil on 17 August 1424, and was captured by the English. He was held prisoner until 1429 at Le Crotoy, paying 200,000 saluts d'or for his ransom. He sold all he possessed to the English, and his fief of Fougères to the Duke of Brittany. After Alençon's capture, the Duke of Bedford, regent of Henry VI, took control of his duchy. He would not regain Alençon until 1449, but remained the titular duke in the eyes of the French crown. When he left prison, Jean d'Alençon was called "the poorest man in France".