Hoax callers from a radio station in Australia got information from the hospital treating the pregnant Duchess of Cambridge.
King Edward VII Hospital in London received a call from two presenters from Sydney radio station 2Day FM.
Presenters Mel Greig and Michael Christian posed as members of the Royal family - believed to be the Queen and Prince Charles - and were transferred to a nurse who gave them an update on Kate's condition. It was played out live on the radio show.
A spokesman for the hospital said: "This call was transferred through to a ward and a short conversation was held with one of the nursing staff. King Edward VII's Hospital deeply regrets this incident."
Kate, who is expecting her first baby with Prince William, is being treated for hyperemesis gravidarum - extreme morning sickness.
A spokesman for the couple has not commented, and the hospital said telephone protocols are under review.