Question How did Mavis knew Natsu was END

[Angiecakes1990]

This has been on my mind lately ever since I saw Mavis had the END book before she gave it to Lucy and thinking how did she know Natsu was END and I was thinking of that flashback in her story when Zeref mentioned seeing and bringing back his brother but he did not mention who it was and now I''m thinking did Mavis knew all along Natsu was END or could she see a resemblance of Zeref in him I dunno.

 

[Nemispelled]

My guess is that Zeref told Mavis about his history/past back when they still loved each other.

Knowing how much Zeref talks about Natsu, I wouldn't be surprised that he mentioned the identity of his younger brother to Mavis when they were together.

 

[Tempus Fugit]

Mavis is a library rat, maybe her curiosity made her open the book.
It probably happened the same as when Lucy opened the book. The letters came out floating and when she realized the situation, she went to look for the guys.

 

[Raven]

The first page of the book is Natsu dragneel thats how she knew xD

Spoiler