Yeah, I think definitely mixed with Koschei - the Horcrux thing is too big not to figure into it. You could very easily fairy-tale it to where the Hero has to go on a Quest to find the Seven Significant Objects in order to Kill the Evil Mutie Sorceror and Free the Lady. I mean, that's basically Book 7 anyway, minus the Damsel in Distress subplot.

A variant of the story has Vo(r/l)demort as someone's bastard son, and giving him extra Evil points for trying to claim his father's name without acknowledgement, and usurp the legitimate son in the process. Like Maleficent vibes, except with acknowledgement instead of a christening invitation.