User blog comment:CNBA3/My Big Three Theories!/@comment-80.43.181.172-20150217195902/@comment-5303512-20150217232753

It was never said that Igneel destroyed E.N.D, it is that he couldn't kill him.

It is never proven that Natsu is 400 years old though with him being E.N.D that roots that out.

Well Igneel really wanted to make sure E.N.D was not revived so maybe he really is evil. Maybe Zeref made E.N.D too strong for him to properly control and started to deny him.