A director explains what it was like casting Rihanna in his movie: 'She's the queen'

Luc Besson has always had an eye for casting actresses who are mesmerizing on the big screen.

There was Natalie Portman in her breakout role in "Léon: The Professional," model-turned-action star Milla Jovovich in "The Fifth Element," Scarlett Johansson in "Lucy," and for his latest movie, "Valerian and the City of a Thousand Planets," you can add two more names: Cara Delevingne and Rihanna.

Delevingne is one of the leads in this adaptation of the legendary French sci-fi graphic novel, while Rihanna plays a shape-shifting entertainer named Bubble.

Having already become one of the biggest artists in the music industry, Rihanna has moved her attention to movies and TV of late. She played Marion Crane in the latest season of "Bates Motel" and recently wrapped on the female-focused "Ocean's Eleven" movie, "Ocean's Eight."

Besson talked to Business Insider and other press on Monday after showing the trailer for "Valerian," and when Rihanna came up, he pointed out the surprising ease of working with the pop superstar.

"What was amazing was all the entourage is out, she's on the set by herself, totally open, and you can mold her how you want," he said. "There's no distance, nothing. She waits for you to do something with her. She offers herself like clay."

He admits, however, that he was shocked to get her on the set all. It seems she basically never has free time.

"The most difficult thing was trying to catch her to get her on set," Besson said. "I think her schedule is worse than any president in the world - I couldn't believe it. She can land at midnight, work until 2am, and I thought I was busy. But she's the queen."

"Valerian" opens in theaters through STX Entertainment on July 21. See the trailer below: