In 1095, Pope Urban II held the Council of Clermont at Clermont-Ferrand, France.
It excommunicated Philip I of France and Bertrade de Montfort, William's sister, for adultery.
William had been noted as a great supporter of Urban II, and after the death of Geoffrey of Boulogne on 1 May 1095 he was in the running to become Bishop of Paris.
As the queen's brother, he held considerable power and sway over the council that elected him - he was also known for his religious devotion.
Urban II considered Montfort a viable choice for the bishopric, however due to his relations to the excommunicated Philip I he was not chosen.