https://en.wikipedia.org/wiki/Duchy_of_Normandy
The Duchy of Normandy grew out of the 911 Treaty of Saint-Clair-sur-Epte between King Charles III of West Francia and the Viking leader Rollo.The duchy was named for its inhabitants, the Normans.. From 1066 until 1204, as a result of the Norman conquest of England, the dukes of Normandy were usually also kings of England, the only exceptions being Dukes Robert …