Blood and Sunfire. Blood and Sunfire, #1

Blood & Sunfire is a ruthless fantasy romance where two enemy heirs are forced into a bond that was never meant to save them-only to use them. Thalia Ravenspire has been raised on vengeance, forged in the long feud between rival houses. Stellan Aurelith is the Crown's golden heir-disciplined, dangerous, and trained to obey. When the kingdom binds them together with an ancient tether meant to "keep the peace, " neither expects the bond to awaken into something far darker.
and far more powerful. Sent into a crumbling keeper-fort to stop a supernatural breach, Thalia and Stellan discover the truth: the Crown has been feeding a hidden Door for generations-a living hunger beneath the throne that devours secrets, sacrifices, and vows. And their bond isn't just a curse. It's the key. Now the palace itself begins to crack, the Hollowing reaches for the heart of the kingdom, and the only way to survive is to turn their tether into a weapon-and make the Crown fear what it created.
Because when blood and sunfire collide.someone is going to bleed.