Sigourney Weaver has revealed that she will play an entirely new character in the highly-anticipated Avatar sequel from James Cameron.

The new movie - Avatar: The Way of Water - will finally be released this Christmas, some 13 years after the original, with a further three sequels due for release over the next six years.

Weaver's involvement had been shrouded in mystery as her character, Dr Grace Augustine, died in the first movie - but now it has been confirmed that she will play new character Kiri, the adoptive teenage daughter of Jake Sully (Sam Worthington) and Neytiri (Zoe Saldana).

"I think we all pretty much remember what we were feeling as adolescents," Weaver, now 72, told Empire magazine. "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."

Cameron added: "As an acting challenge, it's big. 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.

"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."

Avatar: The Way of Water is due for release on December 16.