Robbie Williams has been unveiled as a new global ambassador for WW, formerly known as Weight Watchers.
The singer and X Factor judge will appear alongside Oprah Winfrey and other WW members in the weight management brand’s For Every Body campaign.
Williams will share his "wellness journey" on social media using the hashtag #MyWhy in a bid to encourage others to share their own reasons for getting healthier in 2019.
The campaign is "based on the insight that everyone has their own reason to get healthy and what makes the most meaningful impact along the journey is everything you gain," WW said.
It said the initiative reflects its evolution, building on the company’s "leading position" as it bids to "deliver a more holistic platform for health and wellness".
Williams has previously talked about his battle with weight, and he also poked fun at himself on his 2013 album Swings Both Ways with a track called No One Likes A Fat Pop Star.
He said: "WW is the first programme that truly feels like it fits with my life."
Mr Williams added: "After my back injury last year, I definitely let my healthy habits slip and I felt as though I let myself and my family down.
"I can’t keep trying the same things and hoping for a different outcome.
"I trust the history of behaviour science that WW has, and I’m proud to be a new ambassador. Hopefully, others will benefit from my experience."
Winfrey said: "I’ve had a better life since being a part of the WW family.
"It’s a constant decision to remain healthy and strong and vibrant. I have a real appreciation for every day when I wake up with a healthy mind and a healthy body."
WW’s president and chief executive Mindy Grossman said: "WW aims to be the world’s partner in wellness: a programme designed for everybody and committed to helping millions adopt healthy habits."
"We are so thrilled to have Robbie join our community and inspire others with his wellness journey, to help our members be their best selves," Ms Grossman said.
WW rebranded from Weight Watchers in September, removing Weight from its name and moving its focus to wellness and health.
The new campaign, which launches globally on December 26 and will see Williams featured comes after the organisation’s survey on global wellness suggested that 90% of adults across the world say that improving their physical, mental and emotional health is one of their goals for 2019.
Gail Tifford, chief brand officer at WW, said: "Our members are the heart of our brand. It’s inspiring to hear their stories and the reasons they want to get healthy - what they call #MyWhy.
"What’s interesting is that we’ve found many of these 'whys' are universal.
"Whether you want to get healthy for your children or for yourself, whether you want to feel confident in a wedding dress or feel empowered on the first day of a new job, WW is Wellness that Works. For Every Body. And that’s the premise of our campaign."