 Duyệt was also involved in internal palace machinations . He became involved in a bitter rivalry with General Nguyen Van Thanh , the viceroy of northern Vietnam and commander of the Center Division ; Thanh was another of Gia Long 's leading generals . Duyệt was assisted in this dispute by Nguyen Huu Nghi , who had been a former confidant of Thanh before defecting . Later , another soldier who had served Thanh was caught mingling in Duyệt 's military camp and was captured . Duyệt claimed that the man confessed to being sent by Thanh to assassinate him . 
