Charlotte says: "My agents approached Warner Bros about me being Hermione.
"Eventually they decided I was too old," she explained."I was 13 at the time, and they needed someone about 11, it was so sad".
Charlotte also talked about the much-awaited fifth Potter book: "I am so excited, I've got my order in. I can't wait!
"I read all the books so many times!"
You can watch Charlotte's full interview with Newsround Showbiz on the CBBC channel on Friday at 6:50 pm.