History of the English and British line of succession
Since William the Conqueror claimed the English throne, succession has been determined by bequest, battle, primogeniture, and parliament. == William I == On his deathbed, William the Conqueror accorded the Duchy of Normandy to his eldest son Robert Curthose, the Kingdom of England to his son William Rufus, and money for his youngest son Henry Beauclerc for him to buy land.
Source: Wikipedia — History of the English and British line of succession (CC BY-SA 4.0)