Caught By The Angel

On their 18th birthday, most of the heir of the throne need to find a mate to become their queen.
Swad, the next king of Celestial kingdom, need to find a mate. Nightmare agree but that was centuries ago, before Swad went insane. But now, Nightmare is not the same anymore and he regret himself for being stupid.
What do you think will happen if Swad finally caught Nightmare?