He's had all he can stand, so MC is already breaking protocol. If they now regard Ifa as "free", she might as well walk up to that overgrown child and slap him. I don't know about how the laws of their land would handle that, but I'd love to see at least this happen.
No definitive proof, and you're too scared to let him provide any. MC can ride the Dragon right into the court like he did to that moron's window. Treat it as his companion, and convince the dragon to do same. It shouldn't be hard if the Dragon already allowed the MC to ride on its back.
As a matter of fact...they should probably convince that little jerk of a Prince to give Dragon riding a try, and let HIM ride it into the courts. There's your @#$%%^&!! proof. Seriously, those people have gone from annoying to just infuriating!