Isabel Marshal

According to Wikipedia and many histories of Wales and the Marches, Isabel Marshal, the daughter of William Marshal, the Earl of Pembroke, is the wife of Maredudd ap Rhys Gryg. There may well have been an Isabel Marshal, and she may well have been the daughter of William Marshall, but the William Marshall, Earl of Pembroke, who is of the right date to be her father is known to have no issue.