Prince William is said to be "furious" after a pair of Australian DJs pretended to be the Queen and Prince Charles and managed to trick staff at the hospital where his wife is being treated into revealing conditions about her condition.
Mel Grieg and Michael Christian of radio station 2Day FM convinced staff to put them through to the Duchess of Cambridge's private nurse.
Despite mimicking the corgis barking and putting on unconvincing English accents, the nurse replied to their questions, saying: "She's sleeping at the moment and has had an uneventful night, she's been given some fluids, she's stable at the moment."
On Thursday a source told The Mirror: "There is a lot of anger about this. Prince William was said to be furious when he found out.
"Kate is vulnerable and weak at the moment and these people think it's funny to make joke out of it?"
Dickie Arbiter, the Queen's former press secretary, told the paper there would be "fireworks" over the prank call.
He added: "This is a shocking breach of security. The Royal Family have been clients of the King Edward VII for many, many years and it beggars belief that a member of the public could call up and obtain details of the duchess's medical condition in this way.
"I am sure the Palace will be demanding answers."
Grieg and Christian have apologised for the prank, as has their radio station.
John Lofthouse, chief executive of the hospital said he regretted the breach, but condemned the call as "journalistic trickery".
Lofthouse said: "I think this whole thing is pretty deplorable. Our nurses are caring, professional people trained to look after patients, not to cope with journalistic trickery of this sort."
He said there was no chance the Duchess could have received the call, adding: "Technically I think this was a breach of patient confidentiality, which I very much regret. Having said that, the information which was inadvertently revealed is already in the public domain."