Shadow King by Gav Thorpe
When his family is betrayed and slain, Alith Anar, ill-fated prince of the Nagarythe, is forced to walk a dark path. With the island of Ulthuan in the grip of a civil war with their evil counterparts, the druchii, Alith Anar follows his destiny to become the Shadow King. Hunting his enemies from the darkness, he is now on a quest for vengeance that will never end.