Avatar: The Way of Water, the sequel to the highest-grossing movie of all time, has held its world premiere in London.

Its much-delayed launch comes 13 years after the original sci-fi film, which was released in 2009.

Director James Cameron was joined on the blue carpet in Leicester Square by stars Sam Worthington, Zoe Saldaña, Sigourney Weaver and Kate Winslet.

The Avatar series is set on the lush planet of Pandora where the existence of the Na'vi people is under threat.

Here are some pictures from Tuesday's world premiere in London, and you can find more information about the film further down.

Here are the answers to some burning questions earthlings may have about Avatar: The Way of Water.

The first film followed a paralysed marine Jake Sully (played by Worthington) as he travelled to the planet of Pandora, where he took on an avatar body.

He ended up joining the planet's indigenous population in fighting an attempt by humans to destroy their home to obtain a precious mineral.

The Way of Water is set many years later. Jake now has a family with Neytiri (Saldaña), and it follows their new life on Pandora.

In 2010, a year after the original Avatar, 20th Century Fox (as the company was then called, before it was sold to Disney) said there would be two sequels, and that the first of those would be released in December 2014.

That target proved to be somewhat ambitious. And for the next few years, a regular story out of Hollywood was that the release date had yet again slipped back.

December 2014 became December 2016. Which became December 2017. Which became December 2018. You get the idea. Anyway, it's finally out next week, Friday 16 December 2022.

Cameron threw out one version of an Avatar sequel that, after writing it, he decided didn't deliver.

The Canadian filmmaker also has a life outside cinema, and has spent some time doing deep ocean exploration (although maybe that counts as research for the new film, much of which takes place in and under water).

Cameron also wanted to plot out four sequels. And to take full advantage of new filming developments in the worlds of motion capture and CGI.

Well, it's not Cameron's longest film. That honour goes to Titanic, which clocks in at a hefty 3hrs 15mins.

But Avatar: The Way of Water isn't too far behind. Avatar 2, as it may otherwise be called, has a running time of approximately 3hrs and 12mins.

Slightly less if you dive out at the start of the lengthy end credits!

The stars of the original epic, Sam Worthington and Zoe Saldaña have returned.

So does Sigourney Weaver who - (spoiler alert) - died in the original film.

They are joined by young newcomers Jack Champion, James Flatters, and Trinity Jo-Li Bliss, alongside Oscar winner Kate Winslet.

It's made a total of $2.92bn (£2.39bn) at the global box office, and is the biggest film of all time (unadjusted for inflation).

It briefly lost its title to Avengers: Endgame in 2019, but regained it after Avatar was re-released.

The film is being released in a variety of formats. Including 3D, 2D and Imax. So no one's forcing you to see it in 3D if you don't want to.

But perceived wisdom is that a big part of the original's appeal was its stunningly immersive 3D sequences.

Currently a total of four sequels are planned, including this one.

Avatar 2 is out next week, of course, while Avatar 3 has already been shot, and is due for release in 2024.

Avatar 4 has been partly shot ahead of a planned 2026 release. And Avatar 5 has a finished script. If it's made, and there is a question mark over that, it'll be out in 2028.

The uncertainty is because of the films' cost. The Way of Water had a budget of more than $350m (£287m) which means it needs to be hugely successful at the box office to recoup its money.

If it's a relative failure, it's hard to see Disney putting up hundreds of millions more to finish a series that they think the viewing public may have lost interest in.

In 2018, BBC News revealed that the planned titles were The Way of Water, The Seed Bearer, The Tulkun Rider and The Quest for Eywa.

The Way of Water was finally confirmed in April of this year. Only James Cameron knows whether he will stick with the other titles.

The original was nominated for nine Oscars including best picture, losing out to The Hurt Locker.

Its wins included best production design and best visual effects. Many expect that a similar showing is possible at the 2023 Academy Awards.