The 52-year-old actor - who plays bad Guy Sebastian Shaw in the 'X-Men' origins story directed by Matthew Vaughn - was made to sign a contract because there was so much "secrecy" around the project and had to look at it all in one sitting.
He said: "I got a call, 'X-Men' movie is one of those movies that's completely shrouded in secrecy, it's been really exciting. When I started speaking to them I had to drive over to the Fox lot.
"I happened to be in Los Angeles so I drove over. And they said to me, 'You'll go into a room, in that room there will be a form that you will sign, after you've signed to form the script will be handed to you, after that the door will be locked, you will be able to read the script, then you will be released.'
"I mean literally it was that kind of thing! And I read it and I said yeah! It's great and I love it."
Kevin stars alongside January Jones in the prequel project, and he admits the 60s outfits she wears is reason enough for movie goers to head to the cinema.
Speaking on the Absolute Radio Christian O'Connell Breakfast Show, he said: "She's good looking! And her outfits! They're definitely worth seeing the movie for you know? Check out the outfits."