Stephen King is notoriously hands-off with adaptations of his work if he's not writing them himself. After a few projects messed with his writing in ways he simply couldn't stand (the most famous example of which is Stanley Kubrick's The Shining film), this preference became a brand for the outspoken horror icon. But It: Chapter Two is the exception to the rule. After the first film did his book justice (and wowed fans and critics alike at the box office), King was ready to work with sibling team Andy and Barbara Muschietti on the follow-up. Not only will the film stick close to its source material — it'll have new material added straight from the author.

Speaking with Total Film, director Andy Muschietti explained that learning King enjoyed the first film enough to reach out for the sequel was incredibly important to him. "It was absolutely huge. For me, it would be unthinkable when I was 12 or 13," the director said. So when the author read the first draft of the sequel, made a few notes, and requested the addition of "one all-new scene," Muschietti listened. You don't tell Stephen King that he can't write It.

Another It tidbit from the interview involved the casting of Jessica Chastain as Beverly. After starring in Mama, the Muschiettis' debut feature film, the actress was close to both — and luckily a spitting image of grown-up Sophia Lillis. Since it was always the plan to have two films, one about the grown-ups and one about the kids, Chastain's casting as the adult Bev was discussed before the first film even came out. "The tracking was good, so we started talking about doing the second one before it was released," the director said, "and, in a vaguely unofficial manner, we screened the movie to Jessica." But as the actress recalls, this casting was considered long before that moment. "Andy texted me a picture right after he cast Sophia as Beverly," Chastain said. "There was a side-by-side of Sophia and me. I think he just wrote, 'What do you think?'"

And speaking of those kids, they're making a return in the sequel. The film will flash back to the past — "reopening events," as star James McAvoy puts it — in order to dredge up repressed happenings from the first film's time. That means filming new scenes with young stars who grew up a lot in the two years between movies. But Muschietti had a solution in mind. "From the beginning, we knew that that would be part of the budget, the visual effects to address that," the director said. "So we're going to de-age the kids."

Keep your eyes peeled for de-aged kids and brand-new scenes when It: Chapter Two floats into theaters on Sept. 6.