Fisher hid her pregnancy during Burke and Hare shoot

WENN, Tuesday, October 26, 2010, 4:02am (PDT)

Actress Isla Fisher fooled all her co-stars on the set of new movie, "Burke And Hare," when she successfully hid her pregnancy from them throughout the entire shoot.

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The "Confessions of a Shopaholic" star and her husband, Sacha Baron Cohen, were rumored to have been expecting a second child earlier this year. The secretive couple refused to confirm the news and reports about the birth only surfaced when they were

spotted pushing a stroller around London in September.

Fisher has finally spoken out about her pregnancy, admitting she kept the news quiet during the filming of new movie with Simon Pegg and Andy Serkis, who play infamous British grave robbers.

RELATED: Cohen and Fisher maybe, probably have baby No. 2

The actress didn't tell her co-stars or director John Landis, and spent weeks hiding her morning sickness and her expanding belly.

She wasn't able to wear a tight corset for the period

costume in her condition, but none of her colleagues noticed when she swapped it for a "push-up bra" instead.

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She says, "That was difficult because I was pregnant during the making of the movie, so I didn't really squeeze into it (the corset). I used to pretend I was wearing a corset and then not wear it, just wear a push up bra -- don't tell the director that."

Pegg confirms he had no idea his co-star was pregnant until he saw her sporting a full baby bump months after

the shoot wrapped.

He adds, "I didn't know what was going on. She didn't look pregnant until the last minute. I saw her a couple of months later and she was like a balloon. None of us knew, not even John knew. She hid it well."

Fisher has a daughter, Olive, with Cohen, but they have yet to reveal the gender or the name of their new baby.