User blog comment:Miskos3/Fairy Tail Chapter 486: The Fourth Guest, Review/@comment-4507125-20160524082154/@comment-24734624-20160529022913

Being a human-Etherious-Dragon hybrid is a possibility.

We know for a fact that Zeref modified Humans (or at least one) to become Demons. Hell, Bradman could be Keys 2.0 for all we know. Something may have happened to him before he became a Dragon Slayer.