Super-rich Harry Potter scribe J.K. Rowling is about to get super-richer.

Warner Bros. CEO Kevin Tsujihara has revealed that the author's 54-page book Fantastic Beasts and Where to Find Them will be turned into a three-film series of "megamovies," with Rowling writing the screenplay for at least the first instalment.

"When I say he made Fantastic Beasts happen, it isn't P.R.-speak but the literal truth," Rowling said about Tsujihara in an email to the New York Times that is included in the paper's recent lengthy profile of the Warner Bros. mogul. "We had one dinner, a follow-up telephone call and then I got out the rough draft that I'd thought was going to be an interesting bit of memorabilia for my kids and started rewriting!"

Fantastic Beasts is a short 2001 book that Rowling penned between Harry Potter's fourth and fifth book instalments. News first broke of its planned film adaptation in September, with Rowling confirmed at that time to write the film's script.

"It all started when Warner Bros. came to me with the suggestion of turning Fantastic Beasts and Where to Find Them into a film. I thought it was a fun idea, but the idea of seeing Newt Scamander, the supposed author of Fantastic Beasts, realized by another writer was difficult," Rowling said of the plans for a film at the time. "Having lived for so long in my fictional universe, I feel very protective of it and I already knew a lot about Newt."

"As I considered Warners' proposal, an idea took shape that I couldn't dislodge. That is how I ended up pitching my own idea for a film to Warner Bros."

It is unclear as to whether Rowling plans to pen screenplays for the entire Fantastic Beasts trilogy.

Fantastic Beasts and Where to Find Them is neither a sequel nor a prequel to the existing Harry Potter books, but rather is "an extension of the wizarding world." The book takes place in New York before the start of the first Harry Potter story.