Nicola Roberts, Kimberley Walsh and Nadine Coyle turned out to support Chezza's A Million Lights tour in the capital - making it the first time Nadz has been pictured with the girls in public since their break in 2009.
The trio posted a snap together while watching Cole, who dedicated a Girls Aloud medley to her "special ladies" in the audience.
Sarah Harding was the only member of GA absent from Cheryl's gig, with Digital Spy reporting that she was busy in the studio working on her own solo LP.
Last week, reports claimed that the Popstars: The Rivals group had already recorded their comeback single, as well as shooting the video for the tune.
A source told The Mirror: "The girls recorded tracks with their long-time collaborators Xenomania as early as May this year. Some of them recorded their vocals separately, so they didn’t actually see each other that much during the process.
"Obviously, Nadine has been pretty estranged from the group during their time off, too. But on Tuesday (2nd October), all five were together to film the video for their big return song, which is due out next month."
They added: "It was the last possible opportunity they would all have to get together in time for the release, as Cheryl has been busy rehearsing for her tour and Kimberley’s training schedule for Strictly has been getting more and more intense.”
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