The mum-of-five, who gave birth to daughter Bunny in August, spent Saturday night (18 August) with pal Michelle Heaton - and the pair partied the night away at The Big Reunion Boy Band Tour.
We wonder if there were any awkward encounters between Katie and ex-flings Gareth Gates and Dane Bowers? Eek!
Katie, 36, posed for pictures with Michelle and 911 singer Jimmy Constable at The O2 in London.
Wearing black leather trousers to match her raven hair, Katie showed no signs of giving birth just months ago!
Meanwhile, Michelle also looked fit and fabulous after having a full hysterectomy at the beginning of the month.
The Big Reunion Boy Band Tour kicked off in Sheffield on Friday night (17 October) and features the male acts from both TV series, including Five, 911, A1, Damage, 3T and Blue - who performed with S Club 7's Bradley McIntosh instead of Simon Webbe who is taking part in Strictly Come Dancing.
Gareth Gates, Dane Bowers, Adam Rickitt, Kavana and Kenzie - aka 5th story - are also appearing.
During filming of the ITV2 show, Gareth spoke about his relationship with Katie for the first time.
He said: "We saw each other for three or four months and it was fun, she is a really lovely lovely girl.
"I denied the whole Jordan thing because I was 17, I didn't want my family to find out about my sex life. If I hadn't of lied it wouldn't have been a big deal, my family, friends and fans wouldn't have felt as let down I guess."
During an interview on her reality TV show, Katie revealed that Dane Bowers was the love of her life, and that their split has had a huge impact on every relationship she has had since.
We think her night out must have bought back lots of memories for Katie, who is currently mending her marriage to cheat Kieran Hayler.
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See the other celebrity couples who have welcomed babies in 2014:
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