@Justking14 Well it's not like this is coming from nowhere. Based on the flashback memories of the head maid that looked after the kids. He was even treating the Empress like he had some kind of ownership on her
when she was the Empress and pretty much getting away with it. Just him getting all grab hands on her and yelling at her, that the maid saw, is enough for most heads to roll. That he got away with it could have given him an inflated sense of what he could get away with. And a lot of his stupidness in this plan could also be the green haired boy and the duke's own son seeing his craziness and actively trying sabotage him to save the rest of their family's. Remember, treason means the whole family could be condemned for the duke's actions.