Taking to her Instagram page on Monday, the former X Factor judge touched upon her disbelief and shock as she reassured the Girls Aloud fanbase.
WATCH: A look back at Sarah Harding's life
"Although we knew this day would arrive I am somehow still feeling at a loss for words that our stunning, unique, crazy, quirky, kind and soft hearted girl has departed," Cheryl wrote.
"As I try to navigate my way through these painfully strange and horribly unfamiliar waves of disbelief & finality I am experiencing, I wanted to extend my condolences to all of our GA fans.
"We were like an extended family for so long and we know so many of you by name."
Sarah was diagnosed with breast cancer last year and sadly passed away at the age of 39 following a short battle.
Cheryl posted this picture alongside her statement
Cheryl, 38, added: "I wanted to make sure you knew just how much your love and continued support meant to Sarah through her most vulnerable times. She was so grateful and you really lifted her spirits when she needed you most."
Of her own grief, the pop star remarked: "I also realize so many will be deeply affected by the circumstances of Sarah’s passing… I am sending you all so much love [broken heart enoji] I love you Sarah… farewell."
Sarah's mum Marie broke the sad news on Instagram, writing a statement in memory of her beloved daughter. "It's with deep heartbreak that today I'm sharing the news that my beautiful daughter Sarah has sadly passed away," she said. "Many of you will know of Sarah’s battle with cancer and that she fought so strongly from her diagnosis until her last day.
Girls Aloud were one of the UK's biggest girl groups
"She slipped away peacefully this morning. I'd like to thank everyone for their kind support over the past year. It meant the world to Sarah and it gave her great strength and comfort to know she was loved. I know she won't want to be remembered for her fight against this terrible disease – she was a bright shining star and I hope that’s how she can be remembered instead."
Both Cheryl and Sarah made their names with Girls Aloud. They went on to have more than twenty consecutive top ten singles, including Sound of the Underground, The Promise, Love Machine, Jump and Call The Shots.
After a short hiatus, the band returned in 2012 for the ten-year anniversary and released a greatest hits album and embarked on a final UK and Ireland tour.
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