@Chamcham People have many faces , public , private and persuasive. They'll flick between depending on the situation and how good they are at hiding behind the facade, but it's in moments when it slips and you see what's underneath that are the most impactful.That one moment where he killed without blinking, smile on his face, she knows that is the truth, because a 'normal' person' doesn't wouldn't have that disconnect and you can't reconcile it. He's acting the part of a good person is like instructions from a book, once you see it you can't stop seeing it, or ignore it. The other dukes sons are violent as well but they make more human sense because of the emotions coupled with their actions. This guy's violence was eerily devoid of any real emotion behind it.