Agnes of Ponthieu was the daughter of Count Guy I of Ponthieu

Guy I of Ponthieu

Guy I of Ponthieu was born sometime in the mid to late 1020s. He was the son of Count Enguerrand II and the grandson of Hugh II.-Caught between William of Normandy and Henry I of France:...

. 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 (died 1100). Agnes became count Guy's heiress, and was married to Robert of Bellême

Robert of Bellême, 3rd Earl of Shrewsbury

Robert de Bellême, 3rd Earl of Shrewsbury , also spelled Belleme or Belesme, was an Anglo-Norman nobleman, and one of the most prominent figures in the competition for the succession to England and Normandy between the sons of William the Conqueror...

. Their son William III of Ponthieu

William III of Ponthieu

William III of Ponthieu was son of Robert II of Bellême and Agnes of Ponthieu. He is also called William Talvas....

 succeeded to the county of Ponthieu

Ponthieu

Ponthieu was one of six feudal counties that eventually merged together to become part of the Province of Picardy, in northern France. Its chief town is Abbeville.- History :...

 after the death of Agnes (between 1105 and 1111), and the imprisonment of his father in 1112.

Source

The Gesta Normannorum Ducum

Gesta Normannorum Ducum

Gesta Normannorum Ducum is a chronicle originally created by the monk William of Jumièges just before 1060. In 1070 William I had William of Jumièges extend the work to detail his rights to the throne of England. In later times, Orderic Vitalis and Robert of Torigni Gesta Normannorum Ducum (Deeds...

 of William of Jumièges

William of Jumièges

William of Jumièges was a contemporary of the events of 1066, and one of our earliest writers on the subject of the Norman Conquest. He is himself a "shadowy figure", only known by his dedicatory letter to King William as a monk of Jumièges...

, Orderic Vitalis

Orderic Vitalis

Orderic Vitalis was an English chronicler of Norman ancestry who wrote one of the great contemporary chronicles of 11th and 12th century Normandy and Anglo-Norman England. The modern biographer of Henry I of England, C...

 and Robert of Torigni

Robert of Torigni

Robert of Torigni was a Norman monk and chronicler. He was born at Torigni-sur-Vire in central Normandy, at an unknown date. He entered the monastery of Le Bec in 1128 and became prior there about 1149. He was elected abbot of Mont-Saint-Michel in 1154, and served there until his death.Robert was...

, edited and translated by Elisabeth M. C. Van Houts, Clarendon Press, Oxford, 1995.