She was the daughter of Count Guy I of Ponthieu and Adela.
[1] Enguerrand, her brother, died at a youthful age.
Agnes became count Guy's heiress, and was married to Robert of Bellême.
[1] Their son William III of Ponthieu[1] succeeded to the county of Ponthieu after the death of Agnes (between 1105 and 1111), and the imprisonment of his father in 1112.
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