“Avatar” fans have known for quite some time that Sigourney Weaver is coming back for the upcoming sequel, “Avatar: The Way of Water,” but her return has been a giant question mark, given that her character, Dr. Grace Augustine, died in the first movie. It turns out Weaver is playing not only a brand-new character in “The Way of Water,” but a teenage Na’vi who is the adoptive daughter of Jake (Sam Worthington) and Neytiri (Zoe Saldana). Yes, the 72-year-old Weaver is playing a teenager thanks to the power of James Cameron’s motion-capture technology.

“I think we all pretty much remember what we were feeling as adolescents,” Weaver told Empire magazine, who exclusively revealed the character Kiri. “I certainly do. I was 5’ 10” or 5’ 11” when I was 11. I felt strongly that Kiri would feel awkward a lot of the time. She’s searching for who she is. I was thrilled to be given that challenge by Jim.”

“As an acting challenge, it’s big,” added Cameron, who also directed Weaver in “Aliens.” “We’re gonna have a 60-something actor playing a character [decades younger than] her actual biological age. Sig thought it was all kinds of fun.”

Weaver filmed “Avatar: The Way of Water” as she was turning 70.

Cameron added, “Sigourney just became younger. She looked younger, she had more energy, and she never quite stepped out of Kiri for our whole capture period. She had a glow on her face and lightness in her step and a fun spirit.”

Weaver held her breath underwater for six minutes while filming one scene in the movie. The longer Weaver and other cast members could hold their breath, the more Cameron could film in a single take. The actor trained with elite military divers in order to hold her breath underwater for minutes on end.

The New York Times reported in 2020 that “Weaver and other members of the cast had to learn not to squint or clamp their mouths shut — both natural reactions when you’re submerged — during take after take in a gigantic water tank. She had weights around her waist and professional divers who sped her back to the surface for air at brief, regular intervals.”

“Avatar: The Way of Water” opens in theaters Dec. 16.