The 38-year-old singer, who performed with the “Sound of the Underground” group from 2002 to 2013, broke the news as she shared a selfie from hospital on Twitter on Wednesday (26 August).
“There’s no easy way to say this and actually it doesn’t even feel real writing this, but here goes,” she wrote.
“Earlier this year I was diagnosed with breast cancer and a couple of weeks ago I received the devastating news that the cancer has advanced to other parts of my body.”
In a separate post on Instagram, Harding explained that she was undergoing weekly chemotherapy sessions and thanked her fans for checking in on her while she had been off social media.
“I understand this might be shocking to read on social media and that really isn’t my intention,” she said. “But last week it was mentioned online that I had been seen in hospital, so I feel now is the time to let people know what’s going on and this is the best way I can think of to do so.”
Praising her family and friends for helping her during this difficult time, Harding paid special tribute to “the wonderful NHS doctors and nurses who have been and continue to be heroes”.
“I am doing my very best to keep positive and will keep you updated here with how I’m getting on. In the meantime I hope you’ll all understand and respect my request for privacy during this difficult time,” she said.
Harding rose to fame in 2002 after she won a spot in Girls Aloud on reality competition series Popstars: The Rivals.
During their time together, the British-Irish girl group earned 20 consecutive top 10 singles, four of which went to number one.
The band went their separate ways in 2013, with Harding going on to pursue a career in acting and release her own EP, titled Threads, in 2015. In 2017, she won Celebrity Big Brother.
Reacting to the news, Girls Aloud singer Nadine Coyle commented on her bandmate’s Instagram post: “I love you!!!! You have always been able to achieve miracles when needed!! I am here for the [sic] all the way & always will be!!!”
Seemingly in response to the news, their fellow group member Cheryl tweeted a broken heart emoji.