By August, the English were outside the walls of Paris. The intrigues of the French parties culminated in the assassination of John the Fearless, Duke of Burgundy, by Dauphin Charles's partisans at Montereau-Fault-Yonne on 10 September. Philip the Good, the new duke, and the French court threw themselves into Henry's arms. After six months of negotiation, the Treaty of Troyes recognised Henry as the heir and regent of France. On 2 June 1420 at Troyes Cathedral, he married Catherine of Valois, the French king's daughter. They had only one son, Henry, born on 6 December 1421 at Windsor Castle. From June to July 1420, King Henry's army besieged and took the military fortress castle at Montereau-Fault-Yonne close to Paris. He besieged and captured Melun in November 1420, returning to England shortly thereafter. In 1428, Charles VII retook Montereau, to once again see the English take it over within a short time. Finally, on 10 October 1437, Charles VII was victorious in regaining Montereau-Fault-Yonne.