Comment by aoi on Red_August

@Red_August Exactly. But instead, he chose to simply sit and do nothing. He held the truth and was part of the reason Deon killed his family without knowing anything. He simply used Deon as his sword and was basically playing with the demon king with Deon being some sort of chess piece or prize for them. I understand that he's trying to teach Deon now because he seemingly regrets it, but that doesn't wash away his past actions. 
He could've gotten rid of the duke the moment he found out that the duke had killed his brother whom he cherished, but he didn't.