The model was left heartbroken when she discovered Kieran had embarked on a seven-month sexual relationship with her close friend Jane Pountney.
And, making it all the worse for her, Katie discovered their secret affair just three days after happily announcing she's pregnant with Kieran's second child.
Now, according to The Sun, she's understandably in no mood to celebrate her impending 36th birthday at a planned 'pink and bling-themed'… partly as it was organised by Kieran and Jane.
"It's so awkward," said an insider. "Kieran and Jane had planned everything for the day so Katie could relax."
A source said she now wants to spend the day, which falls on 22 May, relaxing at a private spa before joining her immediate family for a low-key curry dinner.
Katie has not spoken out since 7 May, when she shocked her Twitter followers by announcing Kieran's cheating and her plans to divorce him. She has also not been seen in public since that day when she was photographed arriving at Jane's home to confront her over the affair.
She broke news of her divorce via a series of Twitter messages branding Kieran "disgusting" and saying she was in the "worse [sic] pain ever".
A statement issued later said: "I appreciate most people will have seen my tweets on the subject of my marriage to Kieran.
"I make no apologies for them though it will be appreciated that, sending them immediately after Kieran confirmed to me what he had been doing for the last 7 months, those tweets were a sign of my heart breaking. That he was doing it with a close friend of nearly 20 years is hard to understand."
Kieran has kept quiet on the affair, although Jane - who is married - has publicly admitted that it did happen and she "deeply regrets" it now.
Katie married part-time stripper and builder Kieran in the Bahamas in January 2013 following a whirlwind romance and Christmas proposal. Jane was among the few guests at the beach ceremony.
Katie and Kieran's first child together, Jett, arrived that summer, with the announcement of their second pregnancy coming this month. Katie is also mum to sons Harvey and Junior and daughter Princess from previous relationships.
In an interview published last year, Katie had warned Kieran he would get nothing from her if they split, saying she'd been hurt by men in the past.
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Katie's ex-boyfriends in pictures:
Copyright: PA Images