Sarah had been battling breast cancer and lost her fight Sunday.
Sarah's mom wrote, "It's with deep heartbreak that today I'm sharing the news that my beautiful daughter Sarah has sadly passed away," adding, “Many of you will know of Sarah’s battle with cancer and that she fought so strongly from her diagnosis until her last day."
Sarah got her big break in 2002 on the British talent show, "Popstars: The Rivals" ... where the band was formed. Sarah was picked last of the 5 women, and she sobbed like crazy.
Just 3 weeks after the show ended, Girls Aloud had a number one hit, "Sound of the Underground." Girls Aloud became England's biggest girl group of the 21st Century.
Sarah had plenty of heartbreak ... she was engaged to DJ Tom Crane, but the 4-year relationship ended and she went into a tailspin. In 2011 she went to rehab for depression and alcohol addiction. She said after getting out, "I've been to hell and back ... I'm just glad I survived."
Girls Aloud reunited in 2012 -- their 12th anniversary -- but the group broke up again the following year.
In 2017, Sarah was on "Celebrity Big Brother" and won.
She was diagnosed with breast cancer in 2020. She said at the time doctors told her she would not see another Christmas.
Sarah's mom says cancer should not define her daughter ... "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.”