The French filmmaker has revealed the Diamonds singer has been added to the cast of his forthcoming epic Valerian and the City of a Thousand Planets.

"Rihanna is in VALERIAN!!!!! ....and she has a big part!!" he announced alongside a photo of the singer on Instagram. "I'm Sooo (sic) excited!!!"

The Lucy director didn't specify which character Rihanna will play, but the movie is based on Valerian and Laureline, the classic 1960s graphic novel series by Pierre Christin and Jean-Claude Mezieres.

The Amazing Spider-Man 2's Dane DeHaan and model-turned-actress Cara Delevingne have already been cast as the leads, while Clive Owen will also star in the project, as Commander Arun Filitt.

Valerian and the City of a Thousand Planets will follow two government operatives who are tasked with keeping the peace in a Utopian 28th century Earth. Production is due to begin next year (16), ahead of a July, 2017 release.

Rihanna made her major movie debut in 2012's sci-fi action release Battleship, and she has continued to hone her screen skills with roles in James Franco's comedy This Is The End, movie musical remake Annie and the animated family film Home.

The new movie will serve as a reunion of sorts for Rihanna and her party pal Cara - the stars have been friends since 2011, and earlier this year (15), the supermodel revealed the singer had helped to lift her spirits after losing a role in Beach Boys-themed film All Summer Long.

"I was heartbroken," Cara told The Wall Street Journal Magazine. "With modelling, if someone else gets a job, I'm like, 'Yeah, of course, there are so many better models'. But, with acting, you grow such an attachment to each role."

She turned to Rihanna for a little advice and her words of wisdom helped the runway beauty overcome the setback.

"(She told me), 'Everything happens for a reason'," Cara recalled. "'You are going to call me back up in a week or two, and you are going to say to me, 'You are right'."

The 23-year-old Brit has since been in high demand in Hollywood - the Paper Towns star recently wrapped filming on highly-anticipated comic book adaptation Suicide Squad, alongside Will Smith, Jared Leto, Margot Robbie, Jai Courtney and Viola Davis.