Watch: Sigourney Weaver talks about returning to the Avatar franchise
The 73-year-old star played the ill-fated human scientist Dr Grace Augustine in Avatar, but returns this time around as Kiri — the adopted teenage daughter of Jake (Sam Worthington) and Neytiri (Zoe Saldana).
Weaver said this intriguing casting decision has been on the cards for more than a decade, starting with a meal she had with Cameron just after the first film's success had become clear.
She said: "We actually had lunch in 2010 and just sort of talked about this idea of a character — a girl who was somehow related to Grace and maybe had her curiosity and love of nature, who felt more at home in the forest than she did with people. She was kind of a different girl. So I knew that basic stuff."
Weaver revealed that, in the subsequent years, she was sent the scripts for Avatar: The Way of Water and also the third, fourth and fifth movies.
"What a huge story it is. I'm not saying I'm in all four of them, but I read all four of them," she said.
When approaching the role, Weaver said it was "very challenging" to decide where to pitch her performance as a character around five decades her junior.
"I didn't want to do an imitation of a 14-year-old or do some '14-year-old voice'. So what I had to do was unearth my 14-year-old," she said.
The star added: "I remember that time very vividly because I was this tall when I was 11. So when I was 14, I just wanted to disappear half the time and the other half the time I was outraged about something or other.
"I think Jim encouraged me to improvise and to do whatever I felt like. I would do a preparation off-stage and then I would just let her go. I knew I had to get out of her way."
Weaver said she felt 'incredibly exhilarated' to be able to take on such a profound acting challenge, which is an opportunity only available in the world of performance-capture.
"I wouldn't be able to be 14. John Wayne was never asked to be 14, but I got that opportunity with performance-capture," she said.
Weaver added: "All of the technology falls away and you are just with these great actors, who are playing your father and your mother and your siblings and even a whale-like creature.
"Somehow the material just sets your imagination alight and it becomes your world.
"In a way, I think it's easier than doing a film with make-up and hair and clothes and sets and all of that stuff. I feel it's very freeing."
Avatar: The Way of Water follows Jake and Neytiri as they flee their village when the "sky people" return — led by Stephen Lang as a slightly different Quaritch — to take up refuge with the water-loving Metkayina clan.
As for the future, producer Jon Landau explained that there are big plans for the rest of the franchise, if they're fortunate enough to be able to continue.
"We laid out a roadmap of four movies, each one comes to its own story conclusion and its own emotional resolution, but together they're an even greater character saga," he said.
Landau added: "One of the things history, and even the pandemic, has taught us is that you don't know what the future holds.
"There are more stories to tell, and hopefully world conditions will allow us to tell all of those stories."
Avatar: The Way of Water is in UK IMAX and cinemas from 16 December.
Watch: Trailer for Avatar sequel The Way of Water