The devil you say! He inherited the title "Duke of Normandy" from his dad Robert the Devil in 1035
[DOC] [TLE] Ahnentafel William the Conqueror to Charlemagne [PAR] His mother and father were not married, hence known as "William The Bastard" 
but only ... the time King Philip I inherited the throne in France, William had 
stabilised his position and ... 2 Robert II The Devil,Duke Of Normandy 6th OF 
NORMANDY.