What was the inside story of that year? I'm afraid only the emperor who is hiding in the dark knows it. Even Duan De can't say it clearly!
However, Shen Pingkang, the Immortal Immortal, had a guess in his heart that the Emperor Ming Zun probably knew that the Emperor Ming Zun was going to attack them, otherwise how could the mysterious and silent disappearance disappear? No one was shocked. The original Immortal, the Emperor of Zhenyu, the Emperor of Corpse and others who were also in the dungeon at that time were not aware of his departure.
Moreover, even his Tongtian Hell Treasure was never taken away, which was obviously a premeditated departure, not wanting to disturb anyone, just like Shen Pingkang hundreds of years ago