Abyssal prison!
The divine races had long heard that the abyssal prison was broken after that battle in Crimson City. Even if they didn't know why it broke, a lot of them speculated that it was related to Emodao's promotion into becoming a Sacred Guardian. Some of them even pushed that he broke the prison himself and asked for the position as a reward.
However, Sovereign Tempest was the Dragon Emperor, one of the most respected members of the divine races. He knew exactly why the abyssal prison broke! At first, he was so angry at what Lai Mingjie seemed to say: his son was freed from the abyssal prison when it broke so he wanted to exact revenge!
Who was Sovereign Cinders? He was the most powerful Deputy General and the one that rallied the Imperial Army against Emodao the Bleeding during their campaign before Xu Rouguang was even born. He was revered by most divine races and demonized by none. An epitome of what a child of heaven should be... that was who Sovereign Cinders was!