Lindsay Armaou of B*Witched took to Twitter to post the first images of her group together for over a decade.
[B*Witched reform after 12 years]
"First B*witched photo after 12 years... Weird!" she said.
As previously rumoured, Atomic Kitten's trio are Kerry Katona, Natasha Hamilton and Liz McClarnon, with former member Jenny Frost not rejoining the lineup.
[Members of Atomic Kitten and Liberty X pose together]
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 would 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'.
[L: Atomic Kitten, R: Liberty X]
Liberty X star Jessica Taylor wrote on Twitter today: "OMG today's the day! Arrrggghhh! Can't wait to see everyone! x JT."
Other acts confirmed for The Big Reunion are boybands 5ive and 911 and girl group Honeyz.
[Left: 5ive, Right: 911]
5ive recently made a charity video in support of Breakthrough Breast Cancer.
The Big Reunion airs on ITV2 later this month.
Watch 5ive's charity video below: