The former glamour model was shocked to discover her husband's seven-month affair with close friend Jane Pountney last week, but another pal insists it wasn't too surprising as the pair always indulged in ''sexual banter''.
Katie's former friend Jemma Henley said: ''Kieran and Jane did seem to flirt a lot in front of Katie. They are quite flirty people and there's always sexual banter going on in the house. They would walk around holding hands and no one would think anything of it, especially because of Katie's friendship with Jane and how much Kieran supposedly loved Katie. It would never cross your mind that anything more would happen.''
Katie - who has nine-month-old son Jett with Kieran and is pregnant with their second child - revealed Kieran's ''full blown sexual affair'' with Jane on Twitter last week, which was later confirmed by Jane and her husband Derrick.
Jemma predicts her former pal - who also has children Harvey, 11, Junior, eight, and Princess, six, from previous relationships - will have a tough time getting over the betrayal by her both her husband and good friend of 20 years.
She added to Britain's Star magazine: ''It's going to be ten times harder than her other break-ups because she hasn't just lost her husband - Jane is like a sister to her.''
The actress spoke about raising her 11 year old daughter Matilda in the wake of Heath Ledger's death eight years ago.