4th book is "Benighted'

From nightmares to knighthood, the true war starts now.

Brin has conquered the nightmares that once plagued him, and now his goal is to master the power of his class—illusion.

With a new skill that lets him split his mind and juggle multiple thoughts, his imagination is the only limit. But time is running out.

War looms as four nations unite against the Queendom of Arcaena. The Witch Queen’s undead army threatens to destroy everything in its path. When Brin is summoned by the leader of an order of knights, he’s plunged into a conflict that will shape the fate of the world.