During his absence, Baldwin IV of Hainaut invaded Flanders and pillaged Artois; Sibylla reacted strongly and had Hainaut pillaged in response. The Archbishop of Reims intervened and a treaty was signed. When Theoderic returned in 1150, he took vengeance on Baldwin IV at Bouchain, with the aid of Henry I, Count of Namur and Henry II of Leez, Bishop of Liège. In the subsequent peace negotiations, Theoderic gave his daughter Marguerite in marriage to Baldwin IV's son, the future Baldwin V, Count of Hainaut.