William was the son of
William IX by his second wife
Philippa of Toulouse. He was born in
Toulouse during the brief period when his parents ruled the capital. His birth is recorded in the
Chronicle of Saint-Maixent for the year 1099: ('a son was born to Count William, named William like himself'). Later that same year, much to Philippa's ire, Duke William IX mortgaged Toulouse to Philippa's cousin,
Bertrand of Toulouse, and then left on crusade. William and his mother, Philippa, were left in
Poitiers. When his father, William IX returned from his unsuccessful crusade, he took up with
Dangerose, the wife of a vassal, and set aside his rightful wife, Philippa. This caused strain between father and son until 1121 when William X married
Aénor de Châtellerault, a daughter of his father's mistress Dangerose by her first husband, Aimery. William succeeded to the duchy of Aquitaine in 1126. ==Marriage and issue==