Finished this HA and didn't realize this guy had spawned...he is on top of the scaffolding opposite where the other main npc is. Anyway, he jumped me when I was looking for collectibles and killed my cleric merc fairly quick (level 108). Revived the merc and took him down but make sure to check to see if he spawns you don't want to be surprised by this guy.
Like mentioned make sure to clear everything in this area cause adds are the last thing you want.