The Devil’s Son by Ana Calin

Vampire prince Michael the Bad has a reputation—his breathtaking looks, his force, his control. But there’s a part of him that’s very different. A hell spawn lurks inside him, one that he’d rather keep forever dormant. But the time has come for Michael to face his strongest enemy, and for that he needs to become the beast.
Problem is, the beast will demand something in return—to consume Michael’s fated mate, Angelique Serrano.
In order to win against his oldest enemy, Michael has to give himself completely over to the demon, and sacrifice Angelique to its dark desires. If he doesn’t, the war is lost, along with both their lives. Will Michael the Bad find a way to save his lover, or will he give in to evil, and forever become The Devil’s Son?