Tang Dynasty: the Strongest Emperor's Grandson

Zhenguan four years. Li Er was traveling around the world and when passing by a river, he found a baby floating down the river! In order to survive, Li Qiu showed Li Er his first smile in his life! Many years later. Li Er'an, a boy with a childish face and white hair, was sitting in the court hall, with a holy decree written on bright yellow silk. "Dear grandson, if you don't defeat Byzantium, I will drag you back to inherit the throne!" Thousands of miles away, Li Qiu, who was sitting on the airship inspecting the enemy's situation, looked at the imperial edict in his hand and smiled helplessly. You said, How did he, an abandoned baby who drifted on the Jing River, become the grandson of the Tang Dynasty emperor?