User blog comment:CNBA3/About E.N.D. Thought!/@comment-7418318-20140228113107/@comment-3556212-20140228115010

Zeref implied Igneel couldn't kill "that" person. Why do I have a feeling that END is Natsu?! Since I can't think of any other person Igneel can't kill and that would explain why Zeref knows Natsu. ( ._.)