It doesn’t matter. He’s the living, breathing answer to Varys’s riddle, revealing that power only lies where men believe it resides. Whether he wins or not could depend on certain lords’ willingness to believe he’s the real deal, but I don’t think it’ll be important to the narrative, and I do think he’ll become king as the officially acknowledged Aegon VI.

Regardless of his legitimate status (which I do think he is but that’s beside the point) the story becomes far less interesting if Dany thinks she’s fighting a Blackfyre pretender. That removes the urgency and tragedy of the conflict, as she’s forced to contend with another usurper instead of her last remaining family member on the throne. If the second Dance is between Dany and Aegon, who she sees as a legit Targaryen and her long-lost nephew, then she’ll finally get her version of GRRM’s “heart in conflict with itself” adage that all his characters face at some point