The model discovered she was expecting again shortly after her Bahamas wedding last month, which came after a whirlwind romance with the part-time stripper.
"It has come as a shock. I would be lying if I said I wasn’t nervous because I have experienced miscarriages in the past," she said.
"We are over the moon. A baby wasn’t part of our plans at this stage but anyone who knows me knows I am not one for sticking to rules and plans."
After the news broke, Katie took to Twitter to thank fans for their well wishes.
"Thank you soo much for all the lovely messages xxxx," she said.
Kieran added: "Literally haven't stopped smiling since we found out the News. Been hard to hide it. I am so excited. Thank you for all the nice messages. X"
Katie already has three children - Harvey, 10, whose biological father is Dwight York, and Junior, seven, and Princess, five, with first husband Peter Andre.
> IN PICS: KATIE'S CRAZIEST GET-UPS