I'm not married to the idea that it needs to be confirmed, but Dany is meant to "slay the lie" of the mummer's dragon, if we take the prophecy at its word. I take that to mean she'll either uncover the truth, or someone will reveal it to her and she'll make it public. Well, maybe they won't reveal the full truth (like maybe we'll always be left wondering whether or not he's a Blackfyre), but at least the part where he's a fake.

I have no clue how it could play out or how much of the truth would be uncovered though. Just wanted to mention this, cause im seeing a few people across the thread who seem to doubt that the fact that he's fake will be revealed.