2009 feels like a long time ago now, but cast your mind back and you might remember that little phenomenon called Avatar, James Cameron's CG smash hit which still holds the record for highest box-office gross ever with a comfortable margin of $600 million over the director's other smash-hit, Titanic.

Since then, Cameron has teased us with a promised two sequels, later bumping that up to three, and then again to four, which are set to film back-to-back. It's a tale of delays and woe, but it still looks like Avatar 2 is coming, eventually...

Here's everything you need to know as you wait to return to the alien landscape of Pandora.

Avatar 2 release date: Someday, somehow

To cut a long story short, Avatar 2 is finally going to be released (apparently) on December 17, 2021, having been pushed back from December 2020. A new Avatarmovie will follow every other year all the way until Avatar 5 on December 17, 2027.

Now scheduled to land on Pandora December 17, 2021

But if you want the full story, here goes.

Filming was expected to finally begin in April of 2016 but that just didn't happen. Then it was announced in January 2017 that work on the motion capture would be starting in August 2017, and eventually began in September (eight years after the first movie's release).

The movie was originally scheduled for release in December 2014, with the third film arriving in December 2015, which of course also didn't happen. After the fourth film was added to the plans, they were pushed back to December 2016, 2017 and 2018 releases.

Then, in January 2015, it was announced that Avatar 2 would now be coming in December 2017, with Cameron saying that the "very involved" writing process was to blame for the wait.

Next, in January 2017, Avatar 2 was delayed again, the assumption being that it ran scared after Star Wars Episode 8 slipped from May to December 2017.

Cameron has generally been distinctly non-committal about the delays.

"The important thing for me is not when the first one comes out but the cadence of the release pattern," He told Variety. "I want them to be released as close together as possible. If it's an annual appointment to show up at Christmas, I want to make sure that we're able to fulfil on that promise."

He's also completely chilled out about any delays. "It was a seven-year gap between The Terminator and Terminator 2: Judgment Day, seven-year gap between Alien and Aliens," he told CNN.

Avatar sequel titles: Quite the mouthful?

While we've been calling them Avatar 2, Avatar 3 and so on, there hasn't been any official confirmation on what they will be called.

However, the BBC reported that the films could be called Avatar: The Way of Water, Avatar: The Seed Bearer, Avatar: The Tulkun Rider and Avatar: The Quest for Eywa – which Cameron later confirmed are potential titles, but could be subject to change.

Avatar 2 cast: Who's back?

The core cast of the original Avatar film are all on contract, so Cameron's stars will be back in blue for the sequel when it finally hits.

Zoe Saldana, who will reprise the role of the Na'vi princess Neytiri, had only just appeared in the Star Trek reboot when she starred in the 2009 original film, and thanks to projects like Guardians of the Galaxy, she has become the biggest new star to come out of Avatar – as well as cornering the market for playing aliens of various hues.

Sam Worthington will also return as the human-turned-Na'vi Jake Sully, and it's fair to say that his success hasn't mirrored Saldana's, poor chap.

After the box-office success but critical panning of his Clash of the Titans remake and its sequel, Wrath of the Titans, he's slipped from Hollywood leading man down into into indie projects from his native Australia and supporting roles in action movies like Everest and Sabotage.

Sci-fi goddess Sigourney Weaver and bad guy Stephen Lang will be back too, despite the fact that both their characters died in the first film.