Bride to the Fiend Prince by Rebecca F. Kenney

When her father surrenders to an invading kingdom, Amarylla doesn’t realize she’s part of the treaty until it’s too late. Drugged to prevent resistance, she’s swept away to the dark, tortured kingdom of Terelaus, where she is forced to marry the Fiend Prince. When Amarylla holds a dagger to his throat on their wedding night, she and the Prince come to a tenuous arrangement of their own. But he may not be the greatest danger lurking in the Cursed Palace.