Jessica Alba has confessed that for some time she didn't believe Sin City 2 would ever get made.

The 31-year-old actress returns as stripper Nancy Callahan in Sin City: A Dame To Kill For, Frank Miller and Robert Rodriguez's follow-up to the 2005 neo-noir crime thriller.

But she admitted to Collider.com: "Every six months to a year it was like, 'We're going to do it, when's the next one coming?' And then at a certain point it was just like ok, I just didn't believe it.

"When we actually got the start date and I was there on the set it was like a dream. I was like, 'Am I really here? Are we really here? Ok, just making sure.' So yeah, it was surreal and I ran into Rosario [Dawson] and for all of us it's really cool. The first was like open the doors and this has been, certainly as an artist, the best experience."

The actress revealed the writers created an original story especially for her character, so she could return in the sequel to the hit comic book film.

"Mine is an original story so there wasn't a lot to base it off of, but Frank has been drawing. So it's just crazy. It was neat to see their process, Robert and Frank's, and their collaboration and what they inspire from each other and get out of each other and what they're creating. It's really like the 2.0 version of Sin City and it's pretty amazing."

Sin City: A Dame To Kill For, co-starring Mickey Rourke, Joseph Gordon-Levitt and Josh Brolin, is due out in October.