User blog comment:FairyRaven/Fairy Tail Chapter 413: Book of E.N.D., Review and Commentary/@comment-110.20.77.193-20141222214511/@comment-125.212.122.60-20141222234254

Rogue killed Sting after the events of the Tartarus arc. F-Rogue said it himself, not in the near future he said. Probably 3 to 4 years after the GMG.