Fall of the Lich — James Bailey

Azriel has conquered the continent at last, turning whole populations into undead. Raised as revenants these undead are immortal and still retain their thoughts and memories although their bodies slowly decay around them.
Azriel has stumbled across a living child, a distant relative of his that escaped the slaughter. He chooses to spare this child which causes him to question his own motives.
Azriel raises the child as if he was his own, however his fellow undead grow to learn of the boy and begin to see signs of weakness in their old lord.
Forced to send the boy away out of fear for his safety, Azriel is then himself forced to flee his own realm as his people begin to turn on him.