User blog comment:B214/Chapter 499: Gray & Juvia/@comment-5303512-20160829121430/@comment-1359322-20160829122404

Natsu is END, i don't think there's anything else behind it. You may use what Zeref said in the Tartaros arc to say otherwise, but Mashima is also the guy who wrote Silver has a Demon form, and in the end he had none.