I did a search and only found suggestions that it was Inarius but I don't think that fits. I don't think he could see the future, and I think he was imprisoned shortly after creating Sanctuary, like ancient history. I also don't think Itherael would tell Eirena he was dead.
I mean it all makes sense to me. The prophet was an angel, and he knew something was going to happen 1500 years in the future. Itherael's the only one that can read the Scroll of Fate, and he was one of the few angels that supported humans. It would also make sense that he'd want to hide his identity and interference with sanctuary by claiming he knew of the prophet and that he died long ago.