Rachel McAdams and Abby Ryder Fortson join the Are You There God? It's Me, Margaret movie

Are you there, God? It's Judy Blume fans, giving a collective shriek of joy. The movie version of one of the most beloved books of all time is finally a go — and readers, it's gonna be good.

EW can exclusively announce that Abby Ryder Fortson will take on the eponymous role of Margaret Simon — a sixth-grader going through puberty while looking to the universe for answers to the many questions that adolescence presents — in Are You There God? It's Me, Margaret.

Fortson has appeared in the Ant-Man films as the Marvel hero's daughter, as well as HBO's Togetherness, but this will be the first starring role for the young actress. "Margaret and I are really similar," Fortson, 12, tells EW. "I love her. She's so goofy and awesome. She's all heart and love and just wants to have friends and figure out who she is."

Fortson will be joined on screen by Rachel McAdams as Margaret's mother, Barbara, who is tasked with guiding her precocious daughter through her many (many) quandaries. Announcements on the rest of the Simon family are imminent.

"My readers are always fantasy-casting my books, but I've never done that," says Blume. "But you know it when you see it, and Abby is a natural. And I'm so excited that Margaret got a funny, sexy, sassy mom in Rachel."

Are You There God? It's Me, Margaret was first published more than 50 years ago, and its enduring legacy (and consistently high sales numbers) has long made it a target for adaptation. Despite offering up a few other books for option — Tiger Eyes, Forever — Blume has held steady in her resistance to an screen adaptation of her most iconic work: "I said no, we're never going to film Margaret because every person comes to it with their own ideas about her."

But last year, the author received a very persuasive call from writer-director Kelly Fremon Craig, who was hoping to tackle the project alongside her mentor, legendary producer James L. Brooks. The pitch worked, thanks mostly to Blume's reverence for the pair's previous endeavor, the 2016 indie flick The Edge of Seventeen. She invited Craig and Brooks, who produces through his company Gracie Films, to her home in Key West, Fla., where they shared their vision for the project.

"I'm a gut-feeling kind of person, and I fell in love with them both," Blume explains. "This is a team who cares about the book and understands it — I thought, let's do this while I'm still around to enjoy it."

The Lionsgate film will go into production in April — if all goes according to plan, Blume will be able to join for at least part of the process — and the filmmakers are intent on creating a final product that targets everyone (read: not just adolescent girls). Besides the usual pressures of making a movie in 2021, Craig and her team will be shepherding a story that countless readers hold dear… including their young star, who picked up a copy for the first time as she was preparing to audition for the role of Margaret. "I loved how it speaks not only to girls, but to everyone, all around the world, because we all go through changes growing up," Fortson says. "This book is important because some girls don't get the chance to talk to anyone about their body and what happens to them when it changes, and this book tells them it's going to be okay, you're normal, it just matters who you are inside."

And how is Blume anticipating the feeling of giving Margaret up for someone else's artistic vision after half a century? "It will be fine," she says, "because the book is the book — and it always will be the book."

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