After the death of William the Conqueror, Normandy and England were under separate rule and Robert, Duke of Normandy, sold Cotenin and the isles to Henry, who would eventually become King of England and Duke of Normandy by 1106.:22 The islands remained part of the Duchy of Normandy until 1204, when King Philip II Augustus of France conquered the duchy from King John of England; thanks to Pierre de Préaux, a governor of Rouen who possessed the isles, who decided to support King John, the islands remained in the personal possession of the English king and were described as being a Peculiar of the Crown. The so-called "Constitutions of King John" are the foundation of modern self-government.