 In 1815 , Emperor Gia Long summoned him back in order to suppress widespread rebellions in central Vietnam . In 1819 , Duyệt was in Nghệ An and Thanh Hóa in northern Vietnam putting down revolts for Gia Long . During this time , he joined forces with a former rebel leader from a highlands minority group in Cao Bằng . This man became Duyệt 's adopted son under the name Lê Văn Khôi and his men also rallied to the court . Khoi was then propelled directly into a high @-@ ranking post in Gia Định . During the final four years of Gia Long 's reign , Duyệt ascended to the highest rank in the court , and he and Pham Dang Hung , another southerner , were the only people present as the emperor died . Gia Long decreed that Duyệt take command of five royal regiments . 
