William was the son of Robert Curthose, Duke of Normandy, and his wife Sybilla of Conversano. She was the daughter of Geoffrey, Count of Conversano (in southern Italy). His father, the Duke of Normandy was defeated and captured by his brother Henry I of England at the Battle of Tinchebrai in (1106). Robert Curthose went with Henry I to Falaise where Henry met his nephew the young William Clito for the first time. Henry placed his nephew in the custody of Helias of Saint Saens, Count of Arques. Helias had married a daughter of Duke Robert, his friend and lord. The boy William stayed under the care of Helias until August 1110. At that time the king suddenly sent agents to demand the boy be handed over to him. At the time Helias was away from home. But his servants hid the boy and smuggled him to their master. Helias fled to safety among Henry's enemies.