William Plantagenet, Count of Poitiers was born 17 August 1153 in Normandy, France to Henry II of England (1133-1189) and Eleanor of Aquitaine (1122-1204) and died April 1156 in Wallingford Castle, Berkshire, England, United Kingdom of unspecified causes. Notable ancestors include Henry II of England (1133-1189), William I of England (1027-1087), Charlemagne (747-814), Hugh Capet (c940-996), Alfred the Great (849-899). Ancestors are from France, the United Kingdom, Germany, Belgium, the Netherlands, Russia, Ukraine.

William (17 August 1153 – April 1156) was the first child of Henry Plantagenet (later Henry II of England) and Eleanor of Aquitaine, born in Normandy, 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, Duchess of Saxony, Richard I of England, Geoffrey II, Duke of Brittany, Leonora of Aquitaine, Joan Plantagenet and John of England.

He died aged two 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 an error. His half brother Geoffrey Plantagenet (died 1212), who was born within months of William, did later hold that office, causing the confusion.

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