Another hypothesis I feel like the only reason why the Crown Prince told her not to leave is once again to my other one that whenever he's around her or touch her his powers work and they're more clear to him I'm assuming that he already knows or had a feeling that the Dukes power the one with the black hair and red eyes is being suppressed and healed whenever he's around our female lead so he doesn't want her to run away from him if anything happens in the future because he needs her for his powers. And I'm not trying to say that in a bad way but I feel like he realized being around her is totally different from other Nobles and how she treats him and whenever he does touch her and he reads her mind it's something kind towards him which is something new so he wants to keep her around. But he probably knows that the Duke wants her also and you can tell when they were in the garden area and he grabbed her wrist and he realized that his powers were weakened when he touched her, the Crown Prince stopped him in his tracks and told her that she needed to come along. I'm assuming right there the Crown Prince knew that the Duke also knew that she has some power within her to help both of them it's just that the Crown Prince wants to keep her to himself once again not saying it's in a bad way