Henry of Poitou Abbot of Cluny According to the historian Alfred Richard author of Histoire des comtes de Poitou Henry s identification as a son of William IX was an error Henry first appears as a prior of Cluny in an 1100 charter making him far older than William s children In addition Henry is not named among the children of William IX in the chronicle of Saint Maixent I can t imagine such a prominent individual would ve been overlooked had he in fact been a son of William To my knowledge no early or near contemporary source mentions any illegitimate children for William IX That doesn t mean that he didn t have any it just means none were recognized or important enough to be mentioned Henry s mother certainly wasn t William s most famous mistress Dangereuse who only took up with William around 1113 Raoul de Faye who is sometimes listed as a son of Dangereuse and William was actually Dangereuse s son by her husband She and William don t seem to have had any children together Henry of Poitou was evidently of high birth as mentioned by the Anglo Saxon Chronicle and the Laud Chronicle But he doesn t seem to have been a son of William IX indeed he was closer to William s age in all probability