User blog comment:Renkrisb/The Dragneel Brothers/@comment-117.203.59.128-20150519152015

As, Atlas Flame said that Igneel was unable to destroy E.N.D four hundred years ago.E.N.D and Igneel had a fight.Igneel must' ve sealed the demon, realising that it has human existence, and which in turn has given existence to, now, Natsu Dragoneel after 400 years. Actually, this remains mystery.I am just speculating a lot.But, Igneel wanted Book on E.N.D.Most probably to destroy E.N.D and save Natsu' s existence. I believe Zeref doesn' t have anything to do with Igneel and Natsu' s relationship.