太上皇
After the death of Retired Emperor Trần Thái Tông on April 1, 1277 (in the lunar calendar), Trần Thánh Tông officially began his reign as the sole ruler of Đại Việt, but he decided to pass the throne to Crown Prince Trần Khâm, now Trần Nhân Tông, only one year later. He took up the post of retired emperor on the 22nd day of the tenth lunar month (November 8), 1278.