User blog comment:Ncduru/Biggest Mysteries of FT/@comment-31.132.65.53-20150822104940/@comment-7418318-20150822130413

When the master aked he just laughed and then said it was impossible for him, but not how or why.

And when he talked to Natsu about Acnologia, he didn't mention the mission.

At least that's how it was in the Edolas arc. Maybe he later said something to that effect in on Tenroujima, but certainly not in his name-sake episode.