Castle of Wizardry, by David Eddings.
Penultimate volumes of fantasy cycles tend to be slow affairs, moving the plot along just enough to get the reader to the last book. But in this book, the 4th of the 5-book Belgariad series, stuff happens! Lots of stuff happens!
Garion rises to the challenge of leadership, thrust upon him as his elders are incapacitated. The Orb is returned to the land of Riva, and its bright blue fire reveals that Garion is indeed the long-lost Rivan King. Before this revelation, Garion and Princess Ce'nedra had acknowledged their love for each other, and were planning a wedding. But Ce'nedra's reaction to his Kingship is anger, as the ancient accords now require the two of them to wed. And as much as Ce'nedra cares for Garion, she does not want to be forced to marry him.
The next part of Garion's quest calls for him to slay the evil god Torak, or die trying. He and a small band slip from the camp secretly for him to accomplish this task. In his absence, Ce'nedra choses to don armor and rouse the forces of the surrounding nations to her cause -- battling their main enemy kingdom as a distraction, so that Garion can safely reach the land of Torak.
These "Joan of Arc" scenes of the Princess becoming the Rivan Queen were stirring, and I found her character very fully formed. The showdown with her father is especially memorable. We are left with a standard fantasy scene, forces gathering on one front, and a main character questing on another. But this is not a problem, as the common scene is delivered to us uncommonly well.
This was an excellent read, and I am definitely picking up Book #5 soon.