Makai no Ouji to Hanayome

Pauline has been single since the death of her fiancé six years ago. One day, she receives a marriage proposal from the demon world. To her surprise, it is the prince. She was upset at the sudden offer, but she could not refuse the king's order, so she decided to marry into the demon world alone. However, the man who shows up at the wedding is a boy who is not yet old enough to be married..!