Kul screamed and his hands dropped to his sides as he fell to his knees. Eldain saw the healing light of her magic worming its way into his flesh. Kul's body was swollen with muscle, warped to gross proportions by the Dark Powers he served. The magic of Avelorn filled him, seeking to undo the horrific changes he had willingly accepted. The Everqueen wished to destroy him, but Alarielle would not, for it was anathema to end life when she could restore it.
Eldain saw the northern warlord diminish, as though his entire body was being drained of the corruption that had given him such impossible strength and hatred. The face that was both beautiful and monstrous reshaped itself, losing its magnificence and becoming pugnacious and, worst of all, ordinary...
...yada yada then Slaanesh/tug of war between Slaanesh and Alarielle turns him into a chaos spawn.
Full segment here.