[5] The young Duke William was in danger, as other members of the ducal family were trying to assassinate him to regain power in the duchy, and the Norman barons were rebelling.
Osbern was murdered at Le Vaudreuil in the winter of 1040-1041, while protecting the young Duke in the child's bedroom.
[8] Historians of the Normans disagree on the origin of the benefices held by Osbern,[9] specifically which of them came from his father Herfast and which via his marriage to Emma, daughter of the powerful Count Rodulf of Ivry and sister of Hugues, Bishop of Bayeux.
[10] He possessed land widely spread across Normandy: in the Bessin at Crépon, at Hiémois (near Falaise), near the confluence of the rivers Seine and Andelle, around Cormeilles, in Talou, in Pays d'Ouche at Breteuil, and at La Neuve-Lyre.
Osbern married Emma d'Ivry, daughter of Count Rodulf of Ivry,[3] who was half-brother of Richard I, Duke of Normandy.