Katie and Kieran were enjoying the Big Reunion after party, when her former flames Dane Bowers and Gareth Gates - who now perform together in the band 5th Story - showed up.
The event took place after the band’s gig at the O2, so Katie can’t have been totally shocked to see them there.
According to The Sun, the former glamour model moved towards the front of the dancefloor, close to where Dane was DJing.
“Kieran was following her like a puppy.”
However, while Dane apparently kept his cool, Gareth - who famously dated Katie briefly in 2002 - reportedly wasn’t too happy to see Katie.
“As soon as Gareth saw she was around, he legged it,” the source added.
Earlier this year, Katie was left shocked when she discovered Kieran had been having an affair with one of her close pals, while she was pregnant with his child.
The couple welcomed a daughter, who they later named Bunny, in August.