I figured it out myself.
Using the purging ability on his corpse (from the Purging Wand I got back on Joy Island) did the trick.
I am assuming tho that using that the Necromancy ability "raise bloated corpse" might have also done it. Basically anything that makes a corpse blow up.
PS: Just saw your replies now (despite refreshing the website in advance, weird), sorry :X
Yeah, I don't have Source Vampirism, since I am still underleveled for all the quests attached to getting the other Source abilities besides Spirit Vision (this game sure likes throwing lvl 15 enemies at my lvl 12 bumm).
But yeah, thank you.
Last edited by Buttercheese; 22/09/17 11:16 AM.