'Eternals' star Lauren Ridloff didn't know what they were filming when she shot the movie's massive end-credits scene

• Warning: There are major spoilers ahead for "Eternals."
• Lauren Ridloff appears in one of the film's two end-credits scenes.

Harry Styles made his grand entrance into the Marvel Cinematic Universe at the end of "Eternals." His end-credits scene was shrouded in so much secrecy that not even one of the film's stars was sure what they were shooting.

"In January, we were doing some reshoots and that's when they had added that scene," Lauren Ridloff, who plays the speedster Makkari, told Insider. "I was shocked because I didn't even know exactly what we were shooting until we got there on set that day."

"It was really fun," Ridloff added.

In the end-credits scene, which you can read more about here, Eros (Styles) confronts Makkari, Thena (Angelina Jolie), and Druig (Barry Keoghan) claiming that their friends are in trouble and he knows where to find them.

Ridloff may not have known sure what they were going to film because "Eternals" writer Kaz Firpo told Metro they wrote many versions of the film's two post-credits sequeneces.

"We wrote about nine versions before we settled on what's in the movie," Firpo said. "There's some really spicy ones that always change. It's an evolving process."

In an interview with Cinemablend, director Chloé Zhao said she "kept tabs" on Styles since his appearance in 2017's "Dunkirk" and pitched the idea of introducing him as Starfox along with Pip the Troll to Marvel Studios' president Kevin Feige "a while back."

"I love the idea of getting to know Thanos' brother," Zhao said. "He's an Eternal, our version of him... The idea of him having gone through what the Eternals have gone through, doing their work for the Celestials, is very interesting. And how that might have affected Thanos to become who he is today, I love that idea."

What's next for Makkari? Ridloff says she isn't sure.

Surely, we'll see more of Makkari since in the company of Eros, now. The four need to track down Sersi (Gemma Chan), Phastos (Brian Tyree Henry), and Kingo (Kumail Nanjiani). The trio were kidnapped by Arishem at the film's end for preventing the birth of a Celestial.

Plus, there's that budding romance between Makkari and Druig.

Ridloff told Insider she's not sure what's next for her character in the MCU.

"I mean, who knows?" Ridloff said.

"You know that everything in the MCU and Marvel is always hush-hush and top secret. So, I honestly have no idea and I'm telling the truth. I have no idea what's to come," Ridloff added.

"Eternals" is in theaters now.