Weight Watchers bosses announced the big news on Monday (19Oct15), revealing the media mogul, who has battled body issues for years, now owns 10 per cent of the company and will join its board of executives. Oprah has also agreed to a five-year deal to front new advertising campaigns for the firm as she embarks on a new diet plan.

"Weight Watchers has given me the tools to begin to make the lasting shift that I and so many of us who are struggling with weight have longed for," Oprah writes in a statement. "I believe in the programme so much I decided to invest in the company and partner in its evolution."

Weight Watchers chiefs are aiming to use Oprah's endorsement to transform the profile of the company from a diet firm to a lifestyle brand, "helping people lead a healthier, happier life," according to President and CEO Jim Chambers.

Oprah's investment has already started to pay off - Weight Watchers stock soared from $6 (£3.75) a share to $12.79 (£7.99) shortly after the announcement on Monday.

The 61 year old has been open about her ongoing weight battle over the years, often discussing her ups and downs on her long-running talk show, which ended in 2011. Back in 1988, Oprah showed off a slimmer figure by walking out onstage with a wagon piled high with 67 pounds (30.3 kilograms) of fat to represent the amount of weight she had lost.

However, she struggled to keep the weight off and in 2011, she admitted to veteran U.S. broadcaster Barbara Walters one of her life goals was to "make peace with the whole weight thing".