Yuhuatian and Fengli Dao were the eldest sons of the emperor. Because their biological mother was Concubine Wan Gui, they were sent out of the palace to protect their lives after they were born. Yuhuatian was sent to the temple, but Fengli Dao disappeared on the way.
Many years later, Yuhuatian was sent back to the palace to serve around him because of his relationship with Concubine Wan Guifei.
It was just that the emperor was jealous and wanted to execute him, so "Flying Swords of Dragon Gate" was created.