Charles remained in prison after John II was defeated and captured by the English at the Battle of Poitiers. But many of his partisans were active in the Estates General which endeavoured to govern and reform France in the power-vacuum created by the King's imprisonment while much of the country degenerated into anarchy. They continually pressed the Dauphin to release him. Meanwhile his brother Philip of Navarre threw in his lot with the invading English army of the Duke of Lancaster and made war on the Dauphin's forces throughout Normandy. Eventually on 9 November 1357 Charles was sprung from his prison in the castle of Arleux by a band of 30 men from Amiens led by Jean de Picquigny. Greeted as a hero when he entered Amiens, he was invited to enter Paris by the Estates General, which he did with a large retinue and was 'received like a newly-crowned monarch'.