User blog comment:IamJakuhoRaikoben/Chapter 515: I Am You... You Are Me, Review./@comment-24039234-20161221204107/@comment-7418318-20161222062955

True. With Acnologia there were always the possibilities of it being a freak incidence, it being due to him killing so many Dragons or Zeref being involved.

But thanks to Irene we know for sure that without the parents counteracting it, it'd have happened to all DS (or the 1st and 3rd gen anyway) at some point of the other.