--- Michael Altschul, *A Baronial Family in Medieval England: The Clares,
1217-1314*, Baltimore MD (Johns Hopkins Press) 1965. p 39-40:
"Earl Gilbert the Red left a son and five daughters. Of his daughters by Alice de Lusignan, the elder, Isabella, was born in 1263. In 1297 she was betrothed to Guy, son and heir of William de Beauchamp, earl of Warwick. Guy de Beachamp succeeded his father as earl in 1298, but the projected marriage, although still pending, never took place. Not until 1216 was Isabella married, at the advanced age of fifty-three, to the Gloucestershire baron Maurice de Berkeley, and she died without issue in 1338.