Isla Fisher worried the cast of 'Burke & Hare' thought she was "a bulimic actress from Hollywood" because she hid her pregnancy from them.

The Australian actress - who stars alongside Simon Pegg and Andy Serkis in the comedy movie, based on the real life story of two Victorian mass murderers - kept her pregnancy with British actor Sacha Baron Cohen under wraps while filming earlier this year, and was concerned those around her thought she suffered with an eating disorder because of her terrible morning sickness.

Speaking at the premiere of the John Landis-directed movie at the Curzon Chelsea cinema last night (26.10.10), she joked to BANG Showbiz: "It was troublesome. I was always secretly unlacing my corset and trying to not puke in front of everyone.

"But Simon Pegg has no observational skills at all because I had the worst morning sickness, I was totally ill and I think he just thought I was some bulimic actress from Hollywood and he just ignored it. He never asked!"

'Star Trek' actor Simon joked the 34-year-old beauty was "up and down" on the set but he didn't know why and was surprised to learn she was pregnant with her second child, the sex and name of which remains unknown despite her giving birth in September.

He said: "I didn't know she was pregnant when we were shooting, she kept it a big secret. It was amazing because I saw her a couple of months later and she was like a balloon. It was like she had held it in!

"Deborah the costume designer had been quietly letting her costumes out so she could fit into them. It might explain one of The Days why she was a bit up and down but generally speaking you would never guess."

'Burke & Hare' is released in the UK on October 29.