A BeChic EXCLUSIVE: MEET JENNIFER LOPEZ'S DOUBLE Joselyn Martinez in The Back-Up PlanSure, you may have seen photos of Jennifer Lopez on the set of her upcoming film The Back-Up Plan. But take another look at the image to the left. That's not Jenny from the block. It's Joselyn Martinez- who was a stand-in for J.Lo during eight days of shooting in New York City.

"As a stand-in you get to rehearse all of the scenes the actors will do," says Martinez. "It was mostly 12-13 hour days. I wore high heels everyday because Jennifer used them and we have to be the same height.  I still have nightmares about running late to set." Jennifer Lopez in The Back-Up Plan

The Back-Up Plan- which hits theaters in January 2010- is a romantic comedy where Jennifer Lopez's character conceives twins through artificial insemination and then meets the man of her dreams on the same day!

The Washington Heights native worked close to Jennifer and gave us the 4-1-1 on the star's work ethic. "I noticed she gets really focused even when it's a circus around her. When she was acting, there were cameras all around taking pictures of her," says Martinez. "I loved it when she went to her phone to text after a scene. I share her love for texting!"

J.Lo is known to bring her clan to work and last week was no different. Her sister Lynda was on set with her baby. Joselyn says Mama Lopez was there everyday and Marc Anthony stopped by a few times, but no signs of their twins.

"On the last day, when she wrapped, and a birthday cake was brought out for her, she came over and we hugged and she thanked me," says Martinez who is working on the release of her own album "Movimiento Subterraneo" and has a role in an upcoming film.

For more on Joselyn Martinez click here. -Mercedes Sanchez