[5] Henry placed his nephew in the custody of Helias of Saint Saens, count of Arques, who had married a natural daughter of Duke Robert, his friend and patron.

[7] Helias was at the time away from home, so his household concealed William and smuggled him to their master, who fled the duchy and found safety among Henry's enemies.

[7] William's first refuge was with King Henry's great enemy, Robert de Bellême, who had extensive estates south of the duchy.

He invaded the duchy down the river Seine, and on 20 August 1119 was met by the troops of King Henry at the Battle of Brémule, where the French were decisively defeated.

His cousin, King Henry's son William Adelin, the next day sent him back the horse he had lost in the battle with other "necessities" in a courtly gesture.

Louis brought his case to the pope's attention in October 1119 at Reims, and forced Henry I to justify his treatment of the exiled boy.

[10] King Henry appealed astutely to canon law, however, and the marriage was eventually annulled in August 1124 on the grounds that the couple were within the prohibited degree of kinship.

[12] In January he granted him the royal estates in the French Vexin as a base to attack down the Seine into Normandy, and he was married to Joanna of Montferrat, a half-sister of Queen Adelaide of France.

However, he struck back at Bruges and at the Battle of Axspoele south of the town on 21 June, William, with his Norman knights and French allies, defeated Thierry.

[13] At this point, William was joined by Count Godfrey I of Louvain, and together their armies besieged Aalst on 12 July, with the probable intention of going on from there to reduce Ghent.