Wardrake (Dragon Mage Chronicles Book IV‪)‬

Andrei and Jander return home to the city of Vallerin with the grimmest possible news and tell their king to do what he can to prepare his people for war. Kirin is heading toward the capital with a legion behind him, and he is determined to take revenge both on Andrei and on the apprentice he believes supplanted him in his former master's heart. This time, with the might of an entire dragon army at his command, he very well might succeed.