The Horde King of Shadow by Zoey Draven

The fearsome creature came from across Drukkar’s Sea…and there was a rider on its back.

As a scholar in Dothik’s library, Klara has spent her life trying to understand the strange dreams that have plagued her since she was a child—visions of dragons and a world with no written record. Rejected by her royal bloodline after her mother’s death, Klara hides her chilling secret, knowing her rare magic could get her killed.
But when a dragon suddenly appears in Dothik, those dreams become a monstrous reality.
Sarkin Dirak’zar, king of the Sarrothian horde, cares only about finding heartstones—the dwindling power source for their revered dragons. Ice-cold and merciless, the last thing Sarkin wants is a wife, especially a weak and unwanted princess who likely won’t last one night on dragonback. Yet the key to acquiring heartstones lies in Klara’s visions, and so he gives her a cruel choice: marry him to save her people…or let Dothik burn.

Her first duty as queen? Claim a dragon of her own. What’s even more alarming is that unexpected desire begins to simmer with her beguiling but guarded husband…even though his barbed cage of a heart is only meant to keep her away.