I don't get it why is her Brother mad? 🎭

Maybe he realizes what is happening and ether feels used or angry that he can't protect.

I think he's frustrated that he can't protect his sister and it seems like she's always trying to deal with her problems on her own never relying on him. You'd think being the king of the country would change that but it doesn't.
That's my take on it anyway. ╮(￣▽￣)╭