 In 1417 Henry V invaded Normandy with 40 @,@ 000 men . In April that year Dauphin John died and another shift in power occurred when Isabeau 's sixth and last son , Charles , age 14 , became Dauphin . He was married to Armagnac 's daughter Marie of Anjou and favored the Armagnacs . At that time Armagnac imprisoned Isabeau in Tours , confiscating her personal property ( clothing , jewels and money ) , dismantling her household , and separating her from the younger children as well as her ladies @-@ in @-@ waiting . She secured her freedom in November through the help of the Duke of Burgundy . Accounts of her release vary : Monstrelet writes that Burgundy " delivered " her to Troyes , and Pintoin that the Duke negotiated Isabeau 's release to gain control of her authority . Isabeau maintained her alliance with Burgundy from that period until the Treaty of Troyes . 
