The ‘Loose Women’ panellist has claimed Kieran has been sleeping with their children’s nanny Nikki Brown for over a year.
Katie revealed all in a candid interview with The Sun, telling of how she discovered their affair after finding intimate emails on his phone.
The star has said she now feels nothing but anger towards Kieran, having previously forgiven him for having affairs with her close friends Jane Pountney and Chrissy Thomas in 2014.
While rumours the couple’s marriage was on the rocks have been circulating over the past few weeks, Katie seemed to silence them when social media posts she shared included her husband.
She is now seeking a divorce from the builder, who she married in Barbados in 2013, “for adultery”, but hopes to keep it amicable.
Katie and Kieran have two children, Bunny and Jett, together, while she has two kids, Princess and Junior from her marriage to Peter.
She is also mum to 15-year-old Harvey, who was born after her relationship with footballer Dwight Yorke.
Katie and Kieran only renewed their wedding vows in the Maldives earlier this year, after she took some time out of the limelight to focus on her marriage.
Last year, she admitted how speaking about his previous affairs while promoting her latest book had put a strain on their relationship and took time off from her role on the ‘Loose Women’ panel.
She said at the time: “It’s opened up some wounds. It’s been awful. I thought I’d dealt with it. I was numb when it all happened. I’m quite good at putting up a defence, but it’s been torture.
“I haven’t got any tears to cry. My heart is shattered, it’s broken. We’ve come two and a half years and Kieran is having to re-live it.”
Shortly after Katie discovered his first affairs, she announced she was standing by him, as they underwent therapy together, while he also sought treatment for sex addiction.
She chose not to forgive her friends, however, telling Now magazine last year: “I hope she dies very painfully. If I had a voodoo doll I’d use it every day.”
In the book, she also detailed the moment she thought she’d killed Jane after discovering her and Kieran’s affair.