Inside Linda Blair's Shocking Exorcist Return: 'Nobody Had Any Idea What Was About to Happen' (Exclusive)

Warning: This article contains spoilers for The Exorcist: Believer, in theaters now.

The Exorcist: Believer features many shocking developments — but none hold the surprise element of a cameo in the horror movie.

Near the end of the film, Linda Blair returns as Regan MacNeil alongside her mother in the franchise, Chris MacNeil (Ellen Burstyn).

For fans of the movies, the cameo is a jaw-dropping moment, as Blair previously said she had not been approached to star in Believer or its two planned sequels.

In the classic 1973 original, Blair, now 64, played a young girl who became possessed by a demon after playing with a ouija board. The Exorcist was a critical and commercial success, earning $441 million at the worldwide box office. It was nominated for 10 Academy Awards and became the first horror film to ever be Oscar-nominated for Best Picture.

Burstyn, 90, nabbed an Oscar nomination alongside director William Friedkin, Jason Miller for Best Supporting Actor, and Blair for Best Supporting Actress. It won for Best Screenplay and Best Sound.

The new film sees the return of Chris as she agrees to help a single father (Leslie Odom Jr.) when his daughter and her best friend become possessed.

It's revealed that Chris and Regan have a strained relationship and haven't spoken in years. After a horrific incident involving Chris, Regan comes to her mother's hospital bedside during one of the film's final scenes.

Believer director David Gordon Green (Halloween Ends) describes Burstyn and Blair's onscreen reunion that was 50 years in the making as "a beautiful moment." He reveals that their first take is what made it into the film.

"We did take two just kind of for s---s and giggles, but take one was magic," Green, 48, says.

To preserve the surprise even for his crew on set, Green says he didn't add Blair's name to the call sheet for the day. "Her code name was Bartholomew," he says. "Nobody had any idea what was about to happen."

"It was just a really special moment to be a part of that reunion, to be a part of that legacy, the connection that's so monumental that the two of those performers have," Gordon shares. "Witnessing that reconnection was really amazing."

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As for how he convinced Blair to return, Green says he engaged her in "similar ways" to Burstyn.

"I don't want to just say, 'Hey, actors, do you want to be in my movie? Yes or no? Check one,' " Green explains. "I want to say, 'Here I am, here's who I am, here are my intentions. I'm going to go get creative. I might have something to talk about with you later.' "

Green says Blair, who was just 14 while filming the original, became a consultant on the film, advising Green to "design the production around the psychology for the best wellbeing" of the child actors on set.

"We had many conversations about having a child psychologist on set and what to do during production and what to do after production, what to do upon release of the film," says Green. "And so we were getting to know each other in that kind of ethical, creative standpoint."

Green won't share whether Blair and Burstyn will reprise their characters for two planned sequels, but he says he's excited to "see how far I can take it" as he embarks on completing his new Exorcist trilogy.

"I've got a roadmap of infinite ideas of things that I'd like to do," he says.

The Exorcist: Believer is now in theaters.