User blog comment:FairyRaven/Fairy Tail Chapter 372: Breach, Review and Commentary/@comment-2214433-20140221094034/@comment-7418318-20140221125404

What? You asked a question and I answered :P

But to elaborate: The "evil dad" was already covered by Laxus and the surprising "I am your father!" (or in this case "I am your daughter!") with Gildarts and Cana, so I think another 'surprising' father-child relationship is rather unlikely.

Besides on Tenrou, Zeref didn't seem to recognize Natsu on sight, but only once his name was called. I think a father. That's not really any proof, but I still think a father would have noticed his son right away, especially a son with such an iconic haircolour.