The Fae King’s Assassin by Alisha Klapheke

Kill the Fae king or die.
Raised to cut throats, hunt Unseelie monsters, and ride dragons, Berserker-blooded Revna is the best of the best. But she has been assigned the impossible. Her king demands that she kill the ruthless Fae king.
With no other options, Revna must glamour herself and hide among the Fae king’s bevy of potential mates. But all of her training will be useless if she can’t figure out how to feign love.
Lysanael never wanted to be king of the Fae. Partially because politics disgust him, but mostly because the king must beget an heir. Because of a terrifying secret, he refuses to risk mating and fights to conceal his dark past.
A feigned courtship may be the only way through for both of them, but will their ruse save them or will the plan only tangle their hearts in unimaginable ways?