After Algirdas' death in 1377, Jogaila became the Grand Duke. It is believed that the dynastic disputes that soon erupted between him and his uncle Kęstutis and his cousin Vytautas the Great were largely inspired by Skirgaila. It is known about his travels to the Teutonic Knights in 1379 just a year prior to the controversial Treaty of Dovydiškės. Skirgaila was the chief supporter of his brother Jogaila and helped him to imprison both Kęstutis and Vytautas in Kreva castle during the Lithuanian Civil War (1381–1384). Some historians speculate that Kęstutis' death after a week in prison was in fact assassination carried out by Skirgaila. As a reward for a job well done, Skirgaila received the Duchy of Trakai.