Eidolon (Wraith Kings, #2) by Grace Draven

In a bid for more power, the Shadow Queen of Haradis has unleashed a malignant force into the world. Her son Brishen, younger prince of the Kai royal house, suddenly finds himself ruler of a kingdom blighted by a diseased darkness and on the brink of war. His human wife Ildiko must decide if she will give up the man she loves in order to secure his throne.

Three enemy kingdoms must unite to save each other, and a one-eyed, reluctant king must raise an army of the dead to defeat an army of the damned.

A tale of alliance and sacrifice.