Fantastic Beasts and Where to Find Them producer David Heyman has revealed how he and J.K. Rowling came up with the idea for a Harry Potter prequel.

As most Harry Potter fans know, Fantastic Beasts and Where to Find Them was originally a book — a very tiny book — released for charity in 2001.

Written by J.K. Rowling, Fantastic Beasts and its sister book Quidditch Through the Ages are tiny mock Hogwarts textbooks; Newt Scamander details the fantastic beasts he’s encountered over the years, with little notes scribbled in the margins.

Because of the style of the book, it’s perhaps not surprising that the Harry Potter-adjacent story was originally envisioned as a documentary (or mockumentary).

Related: “Just a smidge”: Overanalyzing the first Fantastic Beasts trailer

Heyman tells SlashFilm, “We were sitting around wondering what else we could do in [the wizarding world], and [producer] Lionel Wigram, who is the person I first brought the first [Potter] book to, thought about maybe doing a documentary about Newt. That idea was floated to Jo, and she responded to doing a film about [that character].”

The long-time Harry Potter producer also admits that while he’s been doing various other projects since the end of the Potter movie franchise, “there was a not-insignificant sadness because [the Potter films] had been such a big part of my life. Jo Rowling created such an incredibly rich and deeply conceived world. What you read in the books is in some ways just the surface of this world.”

It’s been widely assumed that Fantastic Beasts and Where to Find Them will be the first in a series, but not so fast. According to Heyman, “we’ve talked about making a couple, but with all these things — and this may be a failing of mine — I don’t look at them as franchises; I look at them as films. We want to make each film as good as we can because if you don’t, you won’t have a second film or a third.”

Hopefully, Fantastic Beasts will be as good as we’re hoping it will be! The movie is directed by David Yates, stars Eddie Redmayne as Newt, and opens on November 18, 2016.