 While Ermenaud III of Auxerre, Arnulf of Sens, Audri of Autun, and Gerard II of Paris pledged themselves for Lothair, Guerin and Adalbert of Avallon remained with Charles the Bald.In March 841, the Burgundians faithful to Charles accompanied Guerin to Aquitaine, from which they expelled Lothair and Pepin.In May, Guerin, as "dux cum Tolosanis et Provincianis", joined Charles and the king of Bavaria, Louis the German, at Châlons-sur-Marne.