The Order of the Phoenix was published in June 2003, and introduced several new characters including Ravenclaw student Luna Lovegood.

But the film's producers have urged people not to write in to try to apply for any parts.

A spokesperson told CBBC Newsround: "We've only just started production on the fourth film."

She added: "As for the next movie, it's far too early to think about casting.

"We don't have a script, director, start date or casting director and no one will be considered for any role until all these are in place.

"We don't want children to be disappointed, so we're asking them not to write into the studios. It would be a waste of their time."

Warner Bros. also told us that there's no point in trying to write in to be an extra in Goblet of Fire, as they're usually found through local schools or special agencies.