User blog comment:FairyRaven/Fairy Tail Chapter 347: Red, Blue, Blond Hair Fight! Review and Commentary/@comment-2214433-20130816143856/@comment-4829046-20130816145541

Considering that Mashima has been returning to the comedic FT, that might be the case.

But it might be something else as well. Perhaps it means a Demon that was sealed returns to the world and not necessarily meaning the return of a previous character. Or it could mean Zeref makes his move but that's too sudden.