The glamour model has been plagued by people insisting the plasterer-and-stripper, whom she wed in January following a short month-long courtship, have a paternity test to determine whether he fathered the seven-week-old baby, but Katie - who began dating Kieran soon after splitting from Argentinean hunk Leandro Penna - insists there is no need to question her son's parentage.
She lamented to the new UK issue of OK! magazine: ''I'm insulted that people could suggest Kieran should do that - we both are. It's ridiculous and not nice for Jett when he grows up. He's definitely the father, you don't even need to justify it.''
The 35-year-old star gave birth prematurely in August while enjoying a holiday in France and she admits having an emergency Caesarean section surgery in a foreign country ''traumatised'' her.
She explained: ''It was just the worst experience because they also wouldn't let Kieran in the room when I was having the Caesarean. I was being wheeled in and they suddenly told us that he couldn't come in and I'm thinking, 'I need Kieran with me.' It traumatised both of us, but it's made us stronger.''
Katie - who also has son Harvey, 11, with soccer star Dwight Yorke, as well as Junior, eight, and Princess Tiaamii, six, with ex-husband Peter Andre - further opened up about Jett's scary first few weeks of life, revealing he had to be given round-the-clock care following his premature arrival.
She said: ''We had to keep going to the hospital every three hours to feed him ... He was on monitors for two weeks after he was born, but his breathing was fine because the doctors gave me injections before he was born, which made his lungs stronger.''
Perry appeared on James Corden's 'The Late Late Show' on Monday and addressed her long-standing rivalry with Swift.