User blog comment:Miskos3/Fairy Tail Chapter 368: The Third Seal, Review/@comment-5598380-20140124212454

Silver being future Gray is possible now since time-travel is one of the themes of FT.

Theory: Maybe the Eclipse gate from the GMG is not the only one, there is also one in Tartaros' possession. Silver aka Future Gray arrived from the future in X777, when the dragons disappeared, using an Eclipse gate. Then after that, he joined Tartarus. -_-