@Nep Well it was the right thing to do for the protagonist, but it wasn't really necessary for the king to force such a silly convention. If you're talking about the knight then you're right, if not then I disagree.
I pity the princess. Forced to take her own life because her father was too proud to admit any defeat. He probably would have kept the status as king as long as they pledged loyalty to the male lead.
Better to be a vessel state and keep their lives then this end.