User blog comment:SoulRise99/Larcade is the REAL Fairy Heart!?/@comment-7418318-20170307131741

I very highly doubt that Zeref, who's coveting Fairy Heart this much, wouldn't notice it being literally under his nose for decades on end. And I also can't imagine that the King of Magic August woudn't notice either, especially with the fascination he seems to have for Larcade.

Also, if Fairy Heart was extracted from Mavis, then wouldn't she know it?