Blood King Part 1 (Crowns #4) by Nicola Tyche:
 
He doesn’t want the throne. He wants revenge.
A new crown. An old wound. And a reckoning written in blood.

A kingdom built on blood…
Raised a fighter in Rael’s brutal bloodsport arena, Cyrus has only ever known survival. Until one act of defiance topples a tyrant, and one vow of vengeance sparks a revolution. Now, he’s the man a broken realm looks to for hope.

A power he can’t control…
Haunted by his past and driven by revenge, Cyrus grapples with a power that has haunted him since he was a child—a power he doesn’t understand. When a sharp-tongued witch offers to help, her motives are unclear. Trust is dangerous, and so is she.

A throne he didn’t ask for…
Crowned in chaos, Cyrus is thrust into a world of politics, power, and war. New enemies rise. Old ghosts return. And while vengeance may have earned him a crown…

It won’t be enough to keep it.