The liar's crown / Abigail Owen.

"Everything about my life is a lie. As a hidden twin princess, born second, I have only one purpose--to sacrifice my life for my sister if death comes for her. I've been living under the guise of a poor, obscure girl of no standing, slipping into the palace and into the role of the true princess when danger is present. Now the queen is dead and the ageless King Eidolon has sent my sister a gift--an eerily familiar gift--and a proposal to wed. I don't trust him, so I do what I was born to do and secretly take her place on the eve of the coronation. Which is why, when a figure made of shadow kidnaps the new queen, he gets me by mistake. As I try to escape, all the lies start to unravel. And not just my lies. The Shadowraith who took me has secrets of his own. He struggles to contain the shadows he wields--other faces, identities that threaten my very life. Winter is at the walls. Darkness is looming. And the only way to save my sister and our dominion is to kill Eidolon...and the Shadowraith who has stolen my heart." -- Dust jacket.