User blog comment:IamJakuhoRaikoben/Chapter 497: The Winter Mage, Review./@comment-24951162-20160810202218/@comment-5303512-20160816003902

Only Mard Geer stating that E.N.D. creating Tartaros has been stated as false, Nothing else was said about anything regarding E.N.D. Or curses, or Natsu, or Zeref or anything like that.

Also, Zeref had no reason to lie, he never did since Natsu and his reunion on Tenrou Island. Igneel really just protected Natsu from the truth that he is E.N.D. so he would not despair or anything like that.

Also with the books thing, don't people find it odd that only Natsu was shown that he had his book separated from him while all the other Etherious have their books as a part of them the entire time? And with Zeref talking to the book, there is definitely more than meets the eyes, and that we do not know the full details of Natsu's past life before he was transported to the future. Though if he does has a split personality is in question, there is no reason to doubt that his book, while connected to Natsu's life, but also contains his Etherios powers

And Curses, it is shown that it also existed outside of Tartaros with Bradman (who is u confirmed if he is an Etherios) which answers the question that it does not originate from Tartaros or Mard Geer, that remains yet to be confirmed if E.N.D. really did make the curses or not.

And there are other hints as well from Zeref that Natsu would lose it if he had killed someone important to him.