EARLDOM of CORNWALL
William de Mortain, Earl of Cornwall, also Count of Mortain, son and heir. He appears to have been b. before 1084, and to have coveted the Earldom of Kent, held by his uncle, Eudes (1067-97), and, being disappointed thereof, to have rebelled, with Robert de Belleme, against the King in Normandy, in an endeavor to recover that Duchy for Robert, the King's elder brother. They were defeated and taken prisoners, 24 Apr 1106, at Tinchebray, when, being attainted, his honours became forfeited. He m. Adilidis. After many years' imprisonment, he became a Cluniac monk, in 1140, at Bermondsey, where he d., probably sp. [Complete Peerage, III:418-9]