Saer seems to have developed a close personal relationship with his cousin, Robert Fitzwalter (died 1235). In 1203, they served as co-commanders of the garrison at the major fortress of Vaudreuil in Normandy. They surrendered the castle without a fight to Philip II of France, fatally weakening the English position in northern France. Although popular opinion seems to have blamed them for the capitulation, a royal writ is extant stating that the castle was surrendered at King John's command, and both Winchester and Fitzwalter endured personal humiliation and heavy ransoms at the hands of the French.