User blog comment:Mangetsu20/The Hollow Victory and The Cursed Boy (FTC 435,436 - Victory Shout, Memoirs)/@comment-25614737-20150520132041

Knowing Natsu is END was expected, but being Zeref's younger brother is unexpected. I'm certain that since Natsu is confirmed to be a demon bounds him to have a final fight against Gray (Devil Slayer Magic). For some reason, at least we now know that Dragon Slayers are stronger than God Slayers though if this only applies to Natsu.