Isla Fisher pregnant with baby number three!

Isla Fisher is reportedly expecting her third child with hubby Sacha Baron Cohen. Photo: Getty Images

Isla Fisher is pregnant with her third child with husband, comedian Sacha Baron Cohen after being spotted concealing a small baby bump while running errands in London last week.

An insider told Us Weekly that the 38-year-old actress is about "three months along", causing her to pull out of her latest role in Now You See Me 2 to focus on her pregnancy.

RELATED: Isla Fisher welcomes baby number 2!

The source revealed: "Production starts in November and she knew she wouldn't be able to do it."

This will be Isla and the 42-year-old Borat star's third child together.

GALLERY: Homegrown in Hollywood

The couple, who have been married since March 2010, are already parents to daughters Olive, six, and Elula, four.

The actress, who is known for being extremely private, opened up about her two pregnancies previously to Fitness magazine in 2013.

GALLERY: Hollywood bump watch: Who's just announced, who's showing and who's ready to pop?

She said: "I gained 65 pounds with my first baby and 70 with my second. I had severe morning sickness both times, so I mostly ate supersize bowls of white pasta with loads of butter and cheese because that was the only thing that took away the nausea."

Isla revealed she took up yoga to lose her post baby weight, admitting she is most proud of her stomach, "Even though it will never be flat again, it's still my favorite because it reminds me of my greatest achievement: my babies," she said.

Subscribe to New Idea and keep up-to-date with all your favourite celebrities, touching real-life stories, delicious recipes and more each week!