The singer and actress first rose to fame in 2004 as a finalist on the third season of TV singing contest American Idol, where she came in seventh place. She has since gone on to earn acclaim as an actress, making her film debut portraying Effie White in 2006’s Dreamgirls, for which she won an Academy Award.

But Jennifer is adamant that her career could have taken a different route if she had taken American Idol judge Cowell's advice seriously during her time on the show.

"His role on that show was mainly to look at image, I think, and I wouldn't really pay any attention to what he says about vocals. That's not his thing," she told The Telegraph. "At the time Simon told me I was 'Too big, in every way.' I think he meant my hair, my voice, my personality, my songs. I didn't really understand how that was a negative thing. I said, 'Is big not what a star is?'"

Jennifer is now using her experience to help her mentor hopefuls on the rebooted version of The Voice U.K., and believes she has many pearls of wisdom garnered from her time in the industry that she can pass on to her proteges. And while the mother-of-one admits that it will be hard for her to judge the contestants, she is adamant that she will always give her honest opinion.

"If a note goes wrong, my body reacts. I've got sympathy for them, but there's no point lying," she said.

The 35-year-old will be joined by rapper and producer, Tom Jones and Bush frontman Gavin Rossdale on the judging panel for The Voice U.K., which airs from Saturday (07Jan17).