The King of Battle and Blood by Scarlett St. Clair

Their union is his revenge.

Isolde de Lara considers her wedding day to be her death day. To end a years-long war, she is to marry vampire king Adrian Aleksandr Vasiliev, and kill him. But her assassination attempt is thwarted, and Adrian threatens that if Isolde tries to kill him again, he will raise her as the undead.

Faced with the possibility of becoming the thing she hates most, Isolde seeks other ways to defy him and survive the brutal vampire court. Except it isn't the court she fears most-it's Adrian. Despite their undeniable chemistry, she wonders why the king-fierce, savage, merciless-chose her as consort.

The answer will shatter her world.