http://en.wikipedia.org/wiki/Agnes_of_Ponthieu

Agnes of Ponthieu was the daughter of Count Guy I of Ponthieu. Enguerrand, the son of Count Guy, died at a youthful age. Guy then made his brother Hugh heir presumptive, but he also died before Guy . Agnes became count Guy's heiress, and was married to Robert of Bellême. Their son William III of Ponthieu succeeded to the county of Ponthieu after the death of Agnes , and the imprisonment of his father in 1112.