 Robert was a member of the de Grandmesnil family and also identified closely with his mother's Giroie family of Échauffour and Montreuil-l'Argillé, members of which family were vassals as well as rivals of the de Bellême family.Robert's mother eventually retired to become a nun at Montivilliers along with two of Robert's sisters, their brother Hugh providing for them.Hugh, who left Normandy with Robert, returned in time to accompany William the Conqueror at the Battle of Hastings, and subsequently was sheriff of Leicester and held sixty-seven manors at Domesday.