The situation remained in stalemate for some time, with Charles of Blois as de facto duke, but with significant territory still controlled by the Montfortists. Outside events again began to have an effect on the conflict. A plague struck France and the king himself was captured by the English at the Battle of Poitiers in 1356. The French state was virtually paralysed. In 1362, when the younger John de Montfort reached 22 years of age, King Edward permitted him to return to Brittany. His return was conditioned by a covenant, the covenant not to marry without permission, given in pledge of several fortresses. On arrival, John attempted to reach agreement with Charles of Blois to make peace and share Brittany, but Charles's wife Joan urged him to resist and crush John. The war resumed in 1363 when Charles de Blois, assisted by Bertrand du Guesclin, had some successes, but when Bertrand left to take control of strongholds in Navarre and Normandy, Charles's advance halted at the unsuccessful siege of Bécherel. Another opportunity to negotiate an agreement arose, but again Joan blocked negotiations. John de Montfort moved to besiege Auray with renowned English warlord John Chandos. Charles of Blois and Bertrand du Guesclin came to the rescue of the besieged city, but they were decisively defeated at the Battle of Auray on 29 September 1364. This battle marked the end of this long conflict: Charles of Blois was killed and Joan of Penthièvre, finding herself a widow, saw her cause collapse. Du Guesclin was captured and ransomed by Charles V for 100,000 francs.. How many years after John de Montfort's return to Brittany did the war resume?