When it was confirmed yesterday that there would be a brand new Harry Potter book, people got very excited.

It was pretty clear from the announcement that the book was the script for upcoming play Harry Potter and the Cursed Child Parts I & II, but JK Rowling has now underlined that fact.

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"To be clear! The SCRIPT of #CursedChild is being published. #NotANovel," she told her Twitter followers.

That's the script as written by Jack Thorne - in a "Rehearsal Edition" at first and then a "Definitive Collectors Edition" once they've ironed out all the kinks in previews.

It's long-been known that the play is set 19 years after the events of Harry Potter and the Deathly Hallows, and when it was first announced, Rowling made sure everyone knew it wasn't a prequel.

But that message has seemingly already been forgotten, and the author has had to repeat herself a few times since.

When a fan quipped that she should add the #NotAPrequel hashtag to her Twitter bio, she replied: "Along with 'the Horcrux wasn't destroyed in CoS because Harry didn't die #PleaseNeverAskMeThatAgainPlease'."

Asked if she would ever write a prequel, Rowling explained that she already has: the screenplay for Fantastic Beasts and Where to Find Them.

The film is based on her own 2001 book written as fictitious author Newt Scamander.

The adaptation features Scamander (played by Oscar winner Eddie Redmayne) as its main character, and is set in New York City 70 years before the start of Harry's story. It will be released on November 18 this year. 

Watch producer David Heyman talk about Rowling's script for the movie below: