The Ruin of Kings By Jenn Lyons

Kihrin is a bastard orphan who grew up on storybook tales of long-lost princes and grand quests. When he is claimed against his will as the long-lost son of a treasonous prince, Kihrin finds that being a long-lost prince isn't what the storybooks promised.

Far from living the dream, Kihrin finds himself practically a prisoner, at the mercy of his new family's power plays and ambitions. He also discovers that the storybooks have lied about a lot of other things too: dragons, demons, gods, prophecies, true love, and how the hero always wins.

Then again, maybe he's not the hero, for Kihrin is not destined to save the empire.

He's destined to destroy it.