Expulsion

Of course, Neltharion wasn't here to help Illidan and the others. He was here for the Dragon Soul.

Although he had escaped from the battlefield with the Dragon Soul before, after returning to his lair, the influence of the Dragon Soul on him gradually appeared. The completion of the Dragon Soul actually represented Neltharion's complete fall, and evil power began to grow in his body. Not only did it change his appearance, but it even made his sanity lower, and crazy thoughts started taking over his mind.

The tremendous changes in his body brought Neltharion immense pain, forcing him to sleep to alleviate it. Moreover, during this time, he had ordered the goblin engineers who served him to build a set of armor for him to stabilize his body that was beginning to collapse.

But what Neltharion didn't expect was that before the goblins finished forging the armor, his Dragon Soul was stolen while he was sleeping!