The former glamour model made the confession during her An Evening With Katie Price event in Sheffield last week, which Reveal attended.
Katie, 38, spoke in detail about discovering Kieran's affair with her ex-best friend Jane, who was a bridesmaid at Katie and Kieran's January 2013 wedding. The betrayal became public knowledge in May 2014 while Katie was pregnant with Kieran's second child.
She gave Kieran a second chance but has cut Jane out of her life… however that didn't stop Katie recently texting Kieran an unflattering photo of Jane she'd seen online.
Recalling Kieran's reaction, Katie told the crowd: "I was Facetiming him in the bar, because he's with the kids tonight. He said, 'You were out of order sending that, it's been two and a half years, why did you do it?'
"I said, 'Well, I just thought I'd let you know what she looks like now.' She's a pig. I'm not being awful, but really, honestly.
"Why do men do that? Why, when they cheat, do they go for [rough] women? He had to work for Jane. I don't understand it – and I was there, easy!"
Katie also told the audience she'd needed Kieran, 29, to shave his beard so she could look at him again and not think about Jane.
"I couldn't look at him without a beard, because it was the face of the Kieran who cheated on me. It messed my head up. It's not easy but the trick is: you can't bring up the past. I know I sent that picture today, but that's because she looked ugly."
Katie's currently promoting her Reborn autobiography, which recounts her discovery of the affair and how she and Kieran moved in from it. They are parents to son Jett, three, and daughter Bunny, two.
Pick up this week's Reveal magazine, in shops now, for more from our wild night with Katie including the moment she found Kieran and Jane together for the first time, how she confronted them, and her latest boob job.