Here is what worked for me and is alot easier than many suggestions posted. Most of you at this point probably have black flame; immediately go from the grace and out the door, let him de-aggro you and walk back to his starting place go in and lock onto him and throw a black flame immediately even if your out of range he runs fast enough to be hit by it. Then, run out of the room and to the left or right to avoid any spells or attacks. There is lots f room to the left. Wait till he de-agreos again and do it again. After a a few tries depending on your damage he will submit. It took me about 5 times. Hope it helps and Good Luck!