The former glamour model - who split from her husband earlier this week after finding out he had an affair with her best friend - is said to be scared about becoming a mother for the fifth time and she doesn't want to be alone when she gives birth to their second baby.
An insider told The Sun on Sunday newspaper: ''Katie is terrified about the birth and despite everything that has gone on, still wants Kieran there.
''He's been a fool but it's still his child and she doesn't want to go through childbirth alone.
''Jett's birth was a traumatic experience so there's no chance she wants to go through that on her own.''
According to reports, Katie found out about Kieran's affair with Jane Pountney after she saw them kissing on a beach, before getting confirmation after seeing a message on his phone saying: ''Has she left yet? Can't wait to see you.''
A source added: ''Katie was furious about the kiss in Cape Verde on what was meant to be a romantic break for her and Kieran - their first with baby Jett.
''They fobbed her and [Jane's husband Derrick] off, claiming it was a drunken snog, but Katie didn't fall for it ... Then she saw the Whatsapp message on Tuesday - that's when she exploded.
''She was furious and knew immediately that the affair was long-term and sexual. She confronted Kieran who confessed all. She could have forgiven them for a kiss, but not for a full-blown affair.''
Meanwhile, Jane's husband Derrick has reportedly asked Katie not to cash-in on on their heartbreak.
A friend told the Sunday Mirror newspaper: ''Derrick has been begging Katie not to go ahead and speak out with more details about his wife and Kieran.
''He has already been left brokenhearted over the fat that news of the affair has come out.
''He understands Katie is angry but if she gives an interview it will cause more hurt for everybody involved in this torrid situation and certainly won't help rebuild their marriage.''
Take a look back at October's inaugural event.
The film is expected to continue without Mendes' involvement.