Chapter 1. Chapter 2. Chapter 3. South of the Cotentin in the south-west corner of the duchy of Normandy, lay the diocese of Avranches, which included the pagus Abricantinus Avranchin next to the duchy of Brittany [1]. In the midth century, the county then referred to as Mortain was recorded in the hands of Guillaume Comte de Corbeil, son of Mauger, a younger son of Duke Richard I.
Guillaume was banished in by Duke Guillaume II who appointed his uterine half-brother Robert to the county. Thereafter the territory remained under the direct control of the kings of England until Normandy was captured by the Capetian kings of France in the early 13th century. His parentage is established by Orderic Vitalis who calls him " son of Count Mauger " when recording his banishment [11].
Comte de Corbeil. The name of Guillaume's wife is not known. He founded the abbey of Grestain after [18]. The relationship between the two families has not been traced. Orderic Vitalis calls her " Duke Robert's concubine ", and specifies her marriage, referring to her husband as stepfather to Duke Guillaume [24].
She presumably died before her husband founded the abbey of Grestain as she is not referred to in the abbey's confirmation charter dated 14 Nov [25]. She is named as the wife of Herluin in the confirmation charter of the abbey of Grestain, dated 14 Nov [27].
Florence of Worcester names Robert as the brother of King William I " but only on his mother's side " [29]. Geoffrey Richard Driscoll Tobin has suggested that the third and fourth witnesses in the following charter were Robert and Eudes, sons of Vicomte Herluin [31] : " Comes Eudo et nepos eius Gaufridus, Robertus vicecomes et frater eius Eudo…Guichomarus filius Alani vicecomitis… " witnessed a charter dated to relating to the abbey of Saint-Georges de Rennes [32].
