Baldwin I of Jerusalem
Fulk probably accompanied Counts Eustace III of Boulogne and Robert II of Flanders on the First Crusade in 1096, along with his three brothers and father. He received the lordship of Beirut after his relative, King Baldwin I of Jerusalem, conquered it, as related in the anonymous short poem, "Verse on the Illustrious Men of the Diocese of Thérouanne who went on the Holy Expedition":