The close friends will share the silver screen together for the first time in the film from director Luc Besson, based on the graphic novel of the same name.
Cara was confirmed for the flick back in May, and Luc announced Rihanna's involvement via Instagram overnight.
He told fans: "RIHANNA is in VALERIAN!!!!! ....and she has a big part!! I'm Sooo excited!!!"
Um, us too!
Valerian and the City of a Thousand Planets tells the story of a time-traveller (played by Dane DeHaan) and his companion Laureline (played by Cara). Clive Owen is also in the movie.
It's not known yet what Rihanna's role is.
According to The Hollywood Reporter, filming for the movie, inspired by one of France's best-selling comic strips of all time, is scheduled to begin later this year, with a release date of July 2017.
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