Third Prince Cang Shuo had ambitions for the throne for a very long time. He competed against Crown Prince Cang Lin openly after Emperor Cang Wanhe fell gravely ill. He was supported by Fourth, Fifth and Sixth Prince. The Crown Prince was supported by the Second and Seventh Prince. The emperor thought this kind of battle for the throne was perfectly normal and let it happen.
Crown Prince Cang Lin borrowed the power of Xiao Sect in order to suppress the Third Prince. As a counter, the Third Price allied with the Burning Heaven Clan. Emperor Cang Wanhe was extremely angered by the actions of the two prices. Blue Wind Imperial Family has always been careful when dealing with the Four Major Sects in order to maintain independent power and influence in Blue Wind Empire. Borrowing power from the two sects went directly against this principle.
One of the reasons Burning Heaven Clan supported Cang Shuo was due to Burning Heaven Clan Young Master Fen Juecheng. Fen Juecheng wanted to marry Princee Cang Yue and Third Prince Cang Shuo would regularly invite Fen Juecheng to the imperial palace so that Fen Juecheng can meet Cang Yue. The Third Prince would regularly pressure Cang Yue about the marriage proposal to the point that Cang Yue left the imperial palace and ended up in New Moon City.
When Emperor Cang Wanhe's health returned to normal with the help of Yun Che, Cang Shuo lost all his influence. He was later arrested on dozens of crimes including "rebellion" and "patricide" and publicly beheaded.