Norman Kings or Norman «King-Dukes»?

Between 1066 and 1144, as a result of the Norman Conquest of England, Normandy and England shared a ruler for all but 15 of the 77 years - William the Conqueror from Christmas 1066 until September 1087, William Rufus from the autumn of 1096 until August 1100, Henry Beauclerc from the autumn of 1106 until December 1135 and Stephen from his coronation in England until Geoffrey Plantegenêt had completed his conquest of Normandy in 1144. All four rulers were «kings of the English»; the titles att..