User blog comment:Mamerge/What if Natsu is END? And Silver is Future Gray?/@comment-173.35.174.29-20140410121333/@comment-112.204.177.112-20140411151543

I agree too. Here are my speculations: The parents of Gray that died during Deliora's attack must have been Gray's adoptive parents (not biological). Gray's real mother died when she gave birth to Gray. Gray's real father is Silver who is a Ice Devil Slayer. Hopefully later, Gray would realize that he also possesses Ice Devil Slayer powers. It would be cool also in future if Natsu and Gray can do Unison Raid, combining Fire Dragon Slayer powers and Ice Devil Slayer powers.