User blog comment:Omega natsu2/Chapter 413: The Book of E.N.D., Predictions./@comment-4489126-20141210173622/@comment-7418318-20141210181606

But thanks to Zero we know that she was born some 120ish years ago, while Igneel had already fought E.N.D. 400 years ago.

Do you mean that Zeref somehow infused Mavis with what was left of E.N.D. after the battle with the Dragon?