 In 1780 , Duyệt became a eunuch of the 18 @-@ year @-@ old Prince Nguyễn Ánh , the nephew of the slain Nguyễn Lord and the most senior member of the family who survived the revolt by the three Tây Sơn brothers , who seized southern Vietnam from the Nguyễn in 1777 . As a result , Nguyễn Ánh and a few loyalists fled into the dense jungles of the Mekong Delta in the far south . Later , Nguyễn Ánh made Duyệt a Cai <unk> ( " Commander " ) of his bodyguards . From 1777 onwards , the military balance between the Tây Sơn and the Nguyễn fluctuated , as the enemies counterattacked each other frequently . 
