User blog comment:BlackWizardZeref/Fairy Tail: Chapter 436 Memoirs Review with a brief mentioning of Chapter 435 Victory Shout!/@comment-26416024-20150519220151/@comment-26416024-20150520040023

@WikiaContributor

We can debate when Mashima came up with E.N.D. (and I'm sure he came up with Natsu's destiny no later than the Tenrou Island arc but I'm not sure he came up with E.N.D. at the same time) but I don't see anyway that Igneel was ever Zeref's foster father. For starters, Natsu was never raised by Igneel until after his E.N.D. powers and memories were sealed in the Book of E.N.D. and that was way after Zeref revealed his last name as Dragneel. Second, on page 14 of chapter 436, Zeref says "We will talk about the days you spent with Igneel and how I met Mavis some other time". If he was raised by Igneel, he would have said we.