How did the Dark Emperor die? And who was it that killed him?
No one had a certain answer to those questions.
The was once a rumour in the Middle Realm that said that a portion of the powers in the MIddle Realm had been unhappy with the Dark Emperor's reign and they had colluded together and employed some insidious methods to murder the Dark Emperor.
But that rumour had not been widely believed.
For if that had been true, with the kind of absolute loyalty the Night Regime held towards the Dark Emperor, it was impossible that they would not be able to determine who the culprits were through a thorough investigation. If it had really been certain factions among the powers in the Middle Realm who murdered the Dark Emperor, it won't just be the Night Regime, but the entire Dark Regions would have been up in arms and would not have spared them. It would have resulted in an highly insane revenge.