Desired By the Fae Prince by Ana Calin

There are two reasons why you should always stay away from Runar Hauldron 1. He can render you a blabbering idiot through his irresistible fae prince beauty. 2. He can consume you through the huge deadly shadow that he casts.
Years ago, his dark powers consumed my parents, leaving me an orphan. Now, every single metahuman that lives outside his castle could be its next victim. His dark powers are going to strike again, that’s for sure. It’s just a matter of when, where, and who they’re going to take. Now, the high spirits have designated me, Sandra of the Ray, to infiltrate Runar’s castle and assassinate him, because apparently I’m the only one who can.
But there’s a problem.
The survival of my race depends on me, and yet here I am, trapped at his castle, with very little will to leave. Runar and I become each other’s prison, and there’s only two ways we can break free—as doomed, guilty lovers, or as mortal enemies. Either way, things aren’t what they seem, and the story about my parents turns out to be a coin with two sides. One of those sides is sharp as hell, and it could kill me, unless I make a really tough choice.