User blog comment:PUNCHURPREGNANT/Gray and Silver Predictions/@comment-24784846-20140531223452/@comment-24339224-20140609045355

well, I'm pretty sure the theory was different than that. The only reference is Acnologia, and it hinted, or showed, that zeref turned him (whoever the dragon slayer was) into acnologia BECAUSE he killed dragons as often as he did. the point is, I am certain that zeref would be needed to turn a devil/demon slayer into a devil/demon. and I have some doubts about the gray summoning deliora.