J.K. Rowling touched on her new Fantastic Beasts movie while being interviewed by Emma Watson for Wonderland Magazine.

Though the Harry Potter author didn’t offer much exciting new information to share concerning her spinoff franchise, which was announced last September, she did offer some backstory and how she came to write the script herself.

“Warner Bros. came to me ages ago and said they wanted to do something with Fantastic Beasts. I could see the potential in it. I knew something about Newt [Scamander, the fictional author of Fantastic Beasts] having written a little something for Comic Relief. I had imagined a little bit of back story for him,” she says.

“So when Warner Bros. came to me and said they wanted to make a film out of the book I had this simultaneous feeling of ‘it has a lot of potential,’ and another feeling of slight panic that ‘I know some things about Newt and I don’t want you to ruin that for me!’ because I knew who he was. So then I went away and sort of dwelt on what I knew about Newt, not intending to write a script but just trying to collect my thoughts so that I could at least give them the backstory I’d imagined, so that their vision was true to what I knew.”

As you would expect from Rowling, once she really started thinking about the idea, pen and paper became her priority. “I really did have one of those moments that always makes you phenomenally excited as a writer; but also that you know is going to end up being a ton of work. I thought, ‘Oh my God, a whole plot’s just descended on me!’ But I wanted to do it as I was really excited about it. I wasn’t really thinking about writing the script myself, I thought, you know, I’ll give them this plot and then – fatally – I sat down and thought ‘I just wonder what it would look like…’ and wrote a rough draft in twelve days!”

The author admits that, having never written a script before, it wasn’t ready for use. “It wasn’t a great draft but it did show the shape of how it might look. So this is how it all started.”

Rowling goes on to say that she didn’t tell Warner Bros. that she wrote the rough draft in 12 days (the secret’s out now!). “I just wanted to get the outline of the story down, and that’s obviously given me a lot to work with going forward.”

In a bit of a playful moment, Rowling tells Watson that she’d like them all to be extras in the movie. “I tell you what I really want. I want you and Dan and Rupert in really heavy make-up in the background of a scene in Fantastic Beasts, and I’ll join you and we’ll sit in a bar room having a laugh for an afternoon,” she said to the actress who played Hermione Granger. “And then we can see if anyone can spot us. I personally would like to be in drag, just to make sure no one can spot me at all.”

Fantastic Beasts will be produced by Harry Potter series producer David Heyman, and the film does not have a release date or cast.

The biggest news out of her interview with Watson for Wonderland was her thoughts on Ron and Hermione’s relationship.