 He was from Guînes in the Boulonnais, the second son of Count Baldwin I of Guînes and distantly related to the counts of Boulogne.Fulk and his brothers Guy, Hugh and Manasses Robert all gave their consent to a privilege their father granted to his monastic foundation of Saint-Médard at Andres in 1084.Fulk and Hugh, then an archdeacon, witnessed a diploma of Manasses, then count, for the same monastery in 1097.