Treaty of Paris 1259
Jersey 1204 "The loss of Normandy to the Plantagenet kings was a reality from 1204, but it was only acknowledged as such by Henry III in 1259. By the terms of the treaty of of Paris made with Louis IX, Henry III secured his position in Gascony, albeit as a vassal of the King of France. In return, Henry III formally quit to Louis IX and his heirs all the land that the King of France actually possessed in the duchy of Normandy and other Plantagenet territories. The significance of this is evident from the fact that Henry III now ceased to use the titles 'Duke of Normandy and Count of Anjou'"
The Channel Islands in the treaty fell under "'islands (if any) which the King of England should hold which are of the kingdom of France'. Islands and all territories in this category, principally Gascony, were hence forth to be held by the king of England in fief, as the duke of Aquitaine, a 'peer of France', of the King of France"