The girl group were seen filming their reformation for upcoming ITV2 show The Big Reunion, reports the Daily Mail.
Kerry Katona, Natasha Hamilton and Liz McClarnon were seen outside the studio with a camera crew in Liverpool yesterday (Tuesday, November 20).
However, former member Jenny Frost was not seen at the reunion, hinting that the comeback will only include the original lineup.
An Atomic Kitten reunion was reported to have been halted earlier this year due to a rift between Katona and Frost, with Frost saying it will not happen with Katona's involvement.
Frost replaced Katona in the group in 2001 after Katona fell pregnant, and just before they experienced their first big success with 'Whole Again'.
5ive, Liberty X and 911 will also be among the bands involved in The Big Reunion on ITV2 next year.
Watch the Atomic Kitten 'Whole Again' music video below: