The star tweeted her followers: ‘Sorry to say me and kieran are divorcing him and my best friend jane pountney bee having a full blown sexual affair for 7 months (sic).’
Though it is unknown whether the tweet is serious or not, fans are still shocked, tweeting back their concern.
One fan wrote: 'OMG not another one’ whilst another refused to believe the news, tweeting: ‘Eh ??? Surely A Joke Or Your Twitter Has Been Hacked!!!!!’
Find out more about Jane Pountney here and read Katie's further tweets detailing the affair.
The tweet comes just days after she announced her fifth pregnancy, her second with her husband of 1 year, 26-year-old Kieran.
The star told Now magazine that she found out she was pregnant after returning from an idyllic holiday in Cape Verde.
She had been feeling unwell during the trip, so decided to take a pregnancy test on her return to the UK. She later revealed that she was ‘terrified’ she was going to lose the child, which she is set to deliver in the summer.
We will give you more news as the story unfolds.