The prince with the help of Chade recovered many items of power and magic and turned to the dark side. He was the one who had the King, he tortured the King. He went to Hel with Chade to gather many items of magic and evil in controlling demons.
Chade's dagger that made him mad was in the Prince's control. The party never learned if the Prince was turned to evil, or if he chose it himself. His death silenced his voice.
When the Prince died his demons disappeared, leading the party to believe that he was in control of them.
The King has buried his body in an unmarked grave facedown to show his contempt for the ungrateful child of darkness.