"Enchanter's End Game" by David Eddings (The Belgariad, Book 5)

The quest was over. The Orb of Aldue was restored. And once again, with the crowning of Garion, there was a descendant of Riva Iron-grip to rule as Overlord of the West.

But the prophecy was unfulfilled. In the east, the evil God Torak was about to awaken and seek dominion. Somehow, Garion had to face the God, to kill or be killed. On the outcome of that dread duel rested the destiny of the world. Now, accompanied by his grandfather, ancient sorcerer Belgarath, Garion headed toward the City of Endless Night, where Torak awaited him. 

To the south, his fiancee, the Princess Ce'Nedra, led the armies of the West in a desperate effort to divert the forces of Torak's followers from the man she loved.

The Prophecy drove Garion on. But it gave no answer to the question that haunted him: How does a man kill an immortal God?

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