Greenmagic — Crawford Kilian

His father was the king. His mother was a slave. Dheribi thought of himself as an outsider -- more than a servant, less than a prince -- until the night he fought to protect a slave girl from a drunken guardsman. Then he learned what it was to be truly an outcast.
He won the fight -- but he had killed a noble, and the penalty was slavery. But before the king passed sentence, he promised Dheribi that if he helped to overthrow the rival city where he would be sold, the king would pardon him and bring him home.
Dheribi's mother made a different promise. The magic of her mountain people was Dheribi's birthright. She swore that if he learned to harness the power within him, he could free all their people -- and the land itself!
So the slave-prince began the perilous quest to cast down his father's enemies and learn the ways of wizards . . . .