A Demon’s Duty by Catherine Lievens

One is a king, the other a bodyguard. There’s no way it can work—right?

Yakim is a bodyguard to the prince of Hell’s consort, and he likes his life as it is. He could do with fewer attempts by the mysterious society to unravel Berith’s work and take over Hell’s throne, but he’s satisfied with his life. As a half-demon, half-human hybrid, he never expected to rise so high in the ranks of the demons serving Berith.
He certainly didn’t expect to catch the eye of the king of Hell.
Lucifer is visiting Berith to meet his new human consort and to talk about the secret society plotting to take his throne. He’d be amused if it didn’t happen at least once a year, but his family might be involved this time, and he dislikes dealing with them.
At his welcome ball, he can’t look away from one of the consort’s bodyguards, and while he realizes how complicated this would become if he attempted to seduce him, he can’t get him out of his head.
Yakim has never aspired to be more than a bodyguard and wouldn’t know where to start being the king of Hell’s consort. The two of them are too different to make any kind of relationship work.

But even if they do manage to make it work, it might not be for long, because the society wants Lucifer’s blood, and they won’t stop until they spill it.