The 42-year-old actress first collaborated with director Cameron on the 1997 multi-Oscar winning disaster movie 'Titanic', and in October, Winslet was revealed to be joining the highly-anticipated 'Avatar' sequels as a character called Ronal.
And Cameron has spilled that Winslet has already done a ''couple of days of rehearsals'' and confirmed she will be playing one of the Sea People in his sci-fi universe.
In an interview with Variety, Cameron said: ''She does, and she's very excited about it. She blazed through for a couple of days of rehearsals and saw the world that we had created, and how we do the work, and she's very excited. She plays a character who's part of the Sea People, the reef people. The one thing she did do is demand that she do all her own water work. I said, 'Alright, that's fine, we'll have to teach you how to free dive.'
''The other actors are up to three- and four-minute breath holds. We've already been doing underwater capture.
''We did a scene last week with six teenagers, well, actually five teenagers and one seven-year-old underwater holding their breath for a couple minutes and acting, actually doing a dialogue scene under water because they speak kind of a sign language.''
Cliff Curtis will also star in the movie as Tonowari, the leader of the Metkayina, the reef people clan, in the Cameron-directed movies - all of which are poised to take place under water.
Cameron revealed, the first movie will be released in 2020, followed by the other three in 20121, 2024 and 2025.
The first 'Avatar' film, released in 2009, still remains the highest grossing movie at the worldwide box office, raking in as much as $2.79 billion.
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