Cheryl, 30, looked incredible in a hot red lace dress at the launch of Kimberley's book, A Whole Lot of History, at the ME London hotel on Monday night.
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The star of the show, meanwhile, showed off her incredible figure in a plunging navy jumpsuit, teamed with striking heels and a deep burgundy lipstick.
Cheryl and Kimberley were joined at the launch by their climbing companion, Denise Van Outen. All three ladies took part in a 2009 celebrity trek up Mount Kilimanjaro for Comic Relief, and have remained close ever since.
Denise and Kimberley, 31, also took part in Strictly Come Dancing in 2012, both reaching the final before losing out to eventual winner Louis Smith.
Newly-single Denise clearly had a ball reuniting with the two singers. "Huge congrats @KimberleyJWalsh can't way to read your autobiography 'A whole lot of history' xxx #proudmate."
Absent from the soiree were Kimberley's other bandmates, Nicola Roberts, Nadine Coyle and Sarah Harding. It is thought that pregnant Nadine, 28, is back at home in LA preparing for the arrival of her first baby. Nicole, meanwhile, appeared to be busy working in the music studio, but she did sent out a message to her friend on her big night.
"Miss Walsh, I hope you're having a lovely time at your book launch tonight… Love u xx," the 27-year-old tweeted.
Among the topics covered in Kimberley's book is Cheryl's very public split from husband Ashley Cole. Kimberley recently revealed to HELLO! magazine that Cheryl encouraged her to include the divorce in her autobiography, and spoke about her strong bond with the star.
"I'm very protective of Cheryl and if she hadn't wanted me to address her split from Ashley (in A Whole Lot of History), I wouldn't have done," she told HELLO!. "But she was quite happy for me to speak about it from my side. In fact, she encouraged it.
"All I could do was be there for her, physically, 24 hours a day. I'd been through it with my sister, so I knew what someone's mental state is like when they've had that sort of shock and I didn't want her to be on her own.
"What was frustrating was that I couldn't understand why it happened, so I couldn't say, 'Well, maybe it's because…' I couldn't help her in that way because I couldn't make sense of it either."
She went on to say, "Cheryl's in a great place now. She lives closer to me when she's here in the UK and that's great… We're friends for life and often joke about how we'll be reminiscing to our kids and grandkids in years to come about how we were in a band and climbed a mountain together."