It's been 20 years since Luc Besson made his outrageous genre-changing sci-fi adventure The Fifth Element. And now he has returned to space with a passion project, Valerian and the City of a Thousand Planets. He feels like he's been preparing for this movie his whole life.

Luc Besson on the set of ValerianLuc Besson on the set of Valerian

"I discovered Valerian at 10," he laughs. "At the time, I had one TV channel in black and white at home, no internet. These two pages every week in my little fanzine were all I had to escape with Valerian and Laureline, two space agents travelling through time and space and kicking alien butts!"

It was while he was shooting The Fifth Element at age 30 that he first had the idea of making a Valerian movie. He had hired Valerian comic book writer Jean-Claude Mezieres to work on the movie, and recounts that one day Mezieres turned to him and asked, "Why are you doing this sh*tty film? Why you don't do Valerian?"

"My first answer was because it's impossible," Besson says. "There are basically two actors and a billion monsters, and I didn't know how we could do it. But every year I looked at the comics again and thought, maybe one day it will be possible. So I started writing."

Then just as he began to think about finally making Valerian, he saw James Cameron's Avatar (2009). "The good news was that, technically, I could see that we can do everything now. The bad news was that my script wasn't good enough. James Cameron pushed all the levels so high. So I started again."

Nine years later, the film is finally in cinemas. Besson says he cast Dane DeHaan and Cara Delevingne as Valerian and Laureline because he wanted actors who were "young and fresh" who would "give the audience the pleasure of discovery". And he says both actors are up for making a sequel. Since the comic was published for 43 years, there's plenty of material.

"It's not just about the money," Besson says. "It's a feeling also. What I need is enthusiasm. I need to have an audience around the world start sending messages, 'Oh my God, please do another one!' If I feel this message, then off I'll go. But Cara and Dane, every time we see each other, we pray we can do another one. We had a really good time. It's like you go on holiday and you want to go back next year to the same place, because you had so much fun."

Watch the trailer for Valerian: