Rogue One director Gareth Edwards has admitted he thought it was a clerical error when he was first approached to helm the Star Wars film.
The British film-maker had just finished production on Godzilla starring Aaron Taylor-Johnson and Bryan Cranston when he got the call and said he was too exhausted to get excited.
He said: "I suspect it was a clerical error and they meant to email someone else.
"I had just finished a big film and was exhausted, I just wanted to have a holiday but I went to Lucasfilm and was not good at auditioning.
"But I got home and was sent an idea and realised it was connecting to A New Hope, my favourite movie of all time.
"I thought 'this is sacrilegious, you can't do this', but then I begged to. It is so surreal to make Star Wars."
He added: "I couldn't sit in the cinema knowing I had the chance to do it but someone else did."
The film is set years before the first-ever Star Wars film, Episode IV, and Gareth joked: "I do Rogue One and George (Lucas) got to do the sequel Rogue Two."
During a Q&A live-streamed on Twitter from George Lucas's visual effects company Industrial Light & Magic in San Francisco, he said he was aware of the pressure to deliver a film in the franchise but added: "You're on set and there are stormtroopers and an X-wing, and you feel four years old again."
Star Felicity Jones, who plays heroine Jyn Erso, said the film gave her a welcome opportunity to escape period dramas.
She said: "It is so great to finally get out of the corset. I'm never going back. This is it now.
"It was full on, Diego (Luna, her co-star) and I would be doing boxing training outside our trailers like we were in Rocky. You throw yourself around these enormous sets."
Rogue One: A Star Wars Story is released in UK cinemas on December 14.