I think it's already been discussed a while back. We didn't sell him, Stoke paid the 1M figure Viktor had negotiated as a release clause. So no sell on fee expected.
CAM are you in the know about the release clause? I ask because as you know you can put virtually anything with in a contract between two parties, the club could still have had a ?1m release clause with a % sell on clause stated within the release clause itself.