A Cage of Magic and Darkness by Marissa Farrar

I freed my half Incubus stepbrother from his cage… now he means to conquer me and my kingdom one sinful touch at a time…

Taelyn…
When my Fae mother married the ruler of our kingdom, moving us into the castle of Highdrift, my new stepbrother was banished.
Now a dark force is working to destroy our lands, leaving us with nothing but desolation in its wake.
When it takes both my mother and the king, I have no choice but to step into their shoes.
A kingdom needs a ruler, and I am to be it.
But there are places in the castle that have been forbidden to me, and when I come across a key in the king’s belongings, I discover a secret room in the dungeon.
I don’t know what draws me down there, but I can’t resist its pull.
It unlocks a magic that’s kept my stepbrother—and his wicked carnal enchantment—a prisoner for years.
He draws power from seduction, strength from sensuality, and, no matter how I fight it, I can’t say no.
Ruarok Loftborn doesn’t only want me. He wants the castle, and my heritage.
A heritage he believes is his alone.

Ruarok…
Half-Fae, half-Incubus, I’ve always struggled to know where I belong in the castle, even as the king’s bastard son.
But when my father brings home his new wife, and gifts me a stepsister, I’m determined to take what’s owed to me.
Except my plot is rumbled, and instead of ruling the kingdom, I’m locked inside a magic cage for a decade…
Until the day comes where the king has fallen and his magic wears off, and the princess Taelyn finds me.
I’ve always had my sights set on the king’s throne, but now Taelyn believes she’s is the rightful heir.
I will do whatever it takes to ruin her, and ensure her people no longer want to crown her queen…
I’ll corrupt the heir.