James Cameron's "Avatar" bowed in theaters in 2009 and since then, expectations are rife about potential sequels. Four follow-ups were confirmed much to fans' delight and expected release dates were announced. "Avatar 2," however, hasn't begun shooting yet and the reason was revealed by Sigourney Weaver, who will reprise her role as Dr. Grace Augustine in the sequels.

Weaver said that Cameron is busy developing the technology that "Avatar 2" and the succeeding installments require, Cinema Blend reported. Weaver added that the director is "trying to make sure that he has really done all the groundwork so when he really starts these four we'll be able to hit the ground running."

Weaver believes that Cameron is "experimenting" on test footages that wouldn't make its way into the "Avatar" movies and are in no way related to the story. But those test footages are vital because it allows the filmmaker to visualize and create the films' special effects, instead of figuring it out in the actual days of filming.

All four "Avatar" sequels will release simultaneously in the month of December in 2018, 2020, 2022, and 2023, The Independent listed. Cameron told Variety that he intends to release the installments "as close together as possible."

Weaver's Grace died in the end of "Avatar," but the actress confirmed last year during an appearance on "The Jonathan Ross Show" that she will come back as a different character, Cinema Blend reported. Cameron, meanwhile, stressed that no one really "dies in a science fiction movie." It remains to be seen what circumstances or form Weaver will return to the "Avatar" franchise.

Weaver was also granted a peek of the three "Avatar" scripts, which she described to Variety as "more amazing than the first one in terms of their scope." She pointed out that the first film established the world of "Avatar" and the relationships within it but in the sequels, Cameron "really gets to play."

Weaver also revealed that filming for "Avatar 2" hasn't started yet, so the December 2018 release date may not be realistic at this point. However, Weaver assures fans that the second sequel will be "very exciting," ComicBook.com reported.

Other main cast members are also returning aside from Weaver, including Sam Worthington (Jake Sully), Zoe Saldana (Neytiri), and Stephen Lang (Colonel Miles Quaritch). Do you think "Avatar 2" will meet its December 2018 release date? How do you think Grace will come back? Sound off in the comments section below!

Tags Avatar 2, James Cameron, Sigourney Weaver