Spent 3 days in Tenebrous and finally got im to spawn. There are 3 coterie camps along the north wall, for those who dont know, he spawned at the middle one of the 3. I easily killed the legionnaires at lvl 57 and didn't pull the named just for the sake of mana conservation. If you do pull them dont worry cuase they are easy. I pulled to the hill behind the two buildings to avoid the adds which are prolific in the area. I pull with ignite blood sent in the pet, lifet(dot, whicever you have at your lvl) and then healed the pet with shadowbond. You just have to keep at it and he will show up. Good Luck
I have found this mob at the North central Cot camp in the Tenebrous. Spawned after I killed enough Legionnaires. Conned light blue to 56 necro. Dropped easy.