The mischievous radio personalities bagged an inside scoop by actually speaking to Middleton's private nurse over the phone and getting exclusive details on her condition.
"She's sleeping at the moment and she has had an uneventful night, she's been given some fluids, she's stable at the moment,'' the nurse told the pranksters, adding "I would suggest that any time after 9-o-clock will be suitable to visit. We'll be getting her freshened up."
The 2Day Fm presenters referred to Kate as their granddaughter during the two-minute call.
King Edward VII's Hospital released a statement saying it "deeply regrets" giving out information about Kate's condition. "This was a foolish prank call that we all deplore," the statement read, "We take patient confidentiality extremely serious and we are now reviewing our telephone protocols.
The announcers and a spokeswoman for the station have since apologized for the hoax after broadcasting it to listeners in Sydney.
Kate Middleton was taken to the London hospital due to a severe form of morning sickness called hyperemesis gravidarum. The confirmation of her first pregnancy followed her admittance to the hospital Monday.
The Associated Press contributed to this report.