Responses
I think he treated her that way because, he's obviously more powerful, so she's been sacrificed for the sake of her kingdom, cause he can wipe them out and both kingdoms know it. Then there's also the fact that apparently he's the actual princess's sworn enemy.
Isn't this supposed to be a peace treaty? Even if you are an asshole, you can't just directly murder the 'hostage' If you want to start a war, there are better ways to do it! And there of probably something going on with him and the actual princess. Is she really frail and sickly, or does she pretend to be. If she is, then it's a good thing she didn't come here. She would have died instantly.