William, Count of Poitiers

William (~1152 - 1156) was the first child of Henry Plantagenet (later Henry II of England) and Eleanor of Aquitaine, born so soon after their marriage (which took place on 18 May 1152) as to set people counting on their fingers: He is said by some historians -- the ones who believe the couple began an affair soon after they met in August 1151 -- to have been born on 17 August 1152 but by others to have been born in 1153.

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 (1151-1212), who was born within months of William, did later hold that office, causing the confusion.