Now, what exactly do we know about the upcoming sequels to Avatar, the biggest box office smash in history?

We know there'll be three sequels, which will qualify Avatar as a true blue Hollywood franchise. James Cameron will be back as director/producer, hoping to earn billions more to add to the $2.8 billion Avatar made back in 2009.

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We also know the first sequel will be released in December 2016; the second in December 2017 and the third in 2018. And we know Avatar II (it doesn't have an official title yet) will be filmed in New Zealand.

That's about it-until now. The buzz has it that Sigourney Weaver will be back.

How's that possible, you ask, since her character, Grace Augustine, was killed off in the original?

It's got a lot to do with friendship, said Cameron. Sigourney will return in all three Avatar sequels in different roles.

"Sigourney and I have a long creative history, dating back to 1985 when we made Aliens," Cameron said. "We're good friends who've always worked well together, so it just feels right that she's coming back for the Avatar sequels."

"Her character of Grace Augustine, as fans know, died in the first movie, so she's playing a different and in many ways more challenging character in the upcoming films. We're both looking forward to this new creative challenge, the latest chapter in our long and continuing collaboration," he said.

He said the sequels will feature a lot of new imagery and a lot of her environments and creatures in Pandora. Much of the action will be set in Pandora and there will be a lot of underwater scenes and surface-water scenes having to do with indigenous ocean cultures on Pandora.

"There's a fair bit of underwater stuff. It's been inaccurately said that the second film takes place underwater. That's not true. There are underwater scenes and surface-water scenes having to do with indigenous ocean cultures that are distributed across the three films."

Cameron said the sequels as a whole are "really the story of his (Jake's) family, the family that he creates on Pandora. His extended family. So think of it as a family saga like The Godfather."

TagsAvatar, sequel, James Cameron, Avatar 2