Pacific Rim 2, the movie no one thought would happen, is definitely happening

A sequel to Pacific Rim will hit theatres in 2018, featuring Star Wars star John Boyega.

The on-again off-again sequel to Guillermo del Toro's Pacific Rim is back on again - and it's got a Star Wars megastar on board.

John Boyega, one of the stand out players in last year's biggest film The Force Awakens, has joined the cast for Pacific Rim 2, Deadline reported.

The sequel to Guillermo del Toro's 2013 film about Earth's battle against giant monsters roaming the planet was thought to have been in production limbo.

But the news about Boyega's casting came with a series of celebratory tweets by del Toro, who will not direct the sequel.

Just landed. I am so happy the news broke! Pacific Rim 2 starts shooting soon!

— Guillermo del Toro (@RealGDT) June 6, 2016

We are preparing some truly great stuff!!

— Guillermo del Toro (@RealGDT) June 6, 2016

The film wasn't a success at the box office, making just US$411 million from a budget of US$191m. But was well received by critics, with an approval rating of 71 per cent on Rotten Tomatoes.

It improved in stature in subsequent years, with fans loving the look of the mech suits worn by soldiers during the film's epic battle sequences.

A monster rampages near the Sydney Opera House in Pacific Rim.

Del Toro kept fans' hopes up with occasional tweets updating them on the sequel, but many had given up on one ever making it to theatres.

Pac Rim 2 cancelled? Don't believe everything you read. It's still going and I'll remain w it in one way or another!

— Guillermo del Toro (@RealGDT) January 11, 2016

Boyega will play the son of the character played by Idris Elba in the sequel, Deadline reported. Pacific Rim 2 comes with a release date of 2018.

"I am very proud and happy to welcome John into a fantastic sandbox. The Pacific Rim universe will be reinforced with him as a leading man as it continues to be a multicultural, multi-layered world," del Toro said in a statement.