The Belgariad Tome 3
Magician's Gambit

A priest of Torak flees across the lands of the west, and two prophecies are now rushing towards one event - one decisive moment which will determine the future of the world. Bound up somehow in these prophecies is Garion - a young lad struggling to develop the sorcery that lies within him. With him is Ce'Nedra. a wilful princess who refuses to accept that sorcery even exists - let alone any silly prophecy.
Yet both must understand and accept their heritage as they follow the magician's trail to a sinister mountain fortress...