User blog comment:FairyRaven/Fairy Tail Chapter 424: Avatar, Review and Commentary/@comment-105.158.135.151-20150316132710/@comment-7418318-20150316162154

That's actually quite convincing. I first thought of Minerva, but Natsu's not the kind of type to draw logical conclusions like that.... that's what he has Lucy for.

But if he heard that Gray killed Frosch in F-Rogue's timeline, that would make even him conclude that they might find him there sooner or later.