User blog comment:BlackWizardZeref/Fairy Tail: Chapter 436 Memoirs Review with a brief mentioning of Chapter 435 Victory Shout!/@comment-4059819-20150519074515/@comment-24039250-20150519080330

It's confusing because a date or year has never been specified. Zeref first, some years later either Igneel and END, or the war....or both at the same time. This is where my theory kicks in. I think it's why Igneel and Zeref sent Natsu into the future. Acnologia fears END and the potential threat it poses. So Natsu was likely sent to the future to X77? where he'd be safe.