Revealing mistake: Lizzie has black nail polish and the same size of nails throughout the entire movie. Supposedly, Lizzie and Isabella are different people. But, when Isabella comes back, you can see she has the same color nail polish and the same size of nails as Lizzie. I don't think it's just a coincidence.
Revealing mistake: Right at the end of the movie, when Lizzie is singing on stage in front of thousands of people, it goes to a shot behind her and you can easily see that she's not actually there.
Revealing mistake: In the scene where Paolo and Lizzie are at the designer's studio, and Lizzie is talking to Paolo while wearing the green outfit, you can see the cord at the back of her neck that made the skirt pop up when she pulled the dangley things in front of her face. (00:43:45)
Answer: No one knows for sure, but he likely lost his career and faced a lot of lifelong humiliation as have previously singers who were found to be secretly lip syncing to someone else's voice.