 In 933 it was annexed to the future Duchy of Normandy, together with the other Channel Islands, Cotentin and Avranchin, by William Longsword, count of Rouen and it became one of the Norman Islands.When William's descendant, William the Conqueror, conquered England in 1066, the Duchy of Normandy and the kingdom of England were governed under one monarch.The Dukes of Normandy owned considerable estates in the island, and Norman families living on their estates established many of the historical Norman-French Jersey family names.