William (August 17, 1153 – 1156) was the first child of Henry Plantagenet (later Henry II of England) and Eleanor of Aquitaine, strangely born on the same day that his father's rival Eustace IV of Boulogne died.

William was a younger maternal half-brother of Marie de Champagne and Alix of France. He was an older brother of Henry the Young King, Matilda of England, Richard I of England, Geoffrey II, Duke of Brittany, Leonora of Aquitaine , Joan Plantagenet and John of England.

He died aged three years at Wallingford Castle, and was buried in Reading Abbey at the feet of his great-grandfather Henry I.

At the time of his death, he had already been given the title of Count of Poitiers. For centuries, the dukes of Aquitaine had held this as one of their minor titles, so it had passed to Eleanor from her father; giving it to her son was effectively a revival of the title, separating it from the dukedom. Some authorities say he also held the title of "Archbishop of York", but this is probably an error. His bastard half-brother Geoffrey Plantagenet (d. 1212), who was born within months of William, did later hold that office, causing the confusion.

Sources

• Robert of Torigny
• Annals of Waverly

1153 births | 1156 deaths | Heirs to the English & British thrones | Heirs apparent who never acceded | House of Anjou | Guilherme, Conde de Poitiers