User blog comment:Natsu11/Zeref and Natsu?/@comment-174.58.132.169-20140623030456/@comment-172.56.28.182-20150518194806

Well now your claim has been denied. Because there is proof in chapter 436 that Zeref and Natsu are blood brothers. Natsu died at a young age for an unknown reason and Zeref did everything he could to revive him. Which he does.