"Magician's Gambit" by David Eddings (The Belgariad, Book 3)

Ce'Nedra, Imperial Princess of Tolnedra, finds herself forced to join a dangerous quest to find the stolen Orb that protects her world from the evil God Torak. Not that she believes in any of that sorcery nonsense. But she must admit that young Garion, his aunt, and his grandfather all appear to possess powers that cannot easily be explained as anything but sorcery. And it doesn't help that she feels a certain closeness with Garion, despite his being a mere farmboy and wholly unsuitable for an imperial princess. Now he is going to a strange tower in the center of all he believed evil, to face some horrible, powerful magician. And she wouldn't be there to watch over him. He might be killed! She'd never see him again...

This copy is in very good condition. First edition, fifth printing -- 1984.