In that year he and his brother Simon left on the Fourth Crusade, but they disagreed with the Siege of Zara (an attack on a Christian city), and refused to take part in the plan to restore Byzantine Emperor Isaac II Angelus in return for Byzantine money and troops.
Amalric rewarded Guy's service by arranging his marriage to la dame de Saete (the lady of Sagette), Helvis of Ibelin, the widow of Reginald, Lord of Sidon (which the French called Saete/Sagette).
Guy later returned home and took part in the Albigensian Crusade led by his brother, Simon de Montfort, 5th Earl of Leicester.
Simon was aiding Guy, who had been injured by a crossbow bolt, at the Siege of Toulouse on 25 June 1218 when he was struck in the head by a stone from a mangonel and killed.
[1] He was taken to the abbey of Haute-Bruyère for burial and the necrology there records a conte Gui de Sagette (count Guy of Sidon).