06/12/2012 13:51 GMT | Updated 06/12/2012 13:51 GMT

Kate Middleton Pregnant: Prince Charles Jokes About Australian Radio Prank

Even a pair of Australian pranksters couldn't dent Prince Charles' joy at the prospect of becoming a grandfather, as he joked with reporters on Thursday who asked him about his daughter-in-law's pregnancy.

He retorted: “How do you know I’m not a radio station?”

The Duchess of Cambridge left the hospital on Thursday. Prince William was on hand to collect his wife, who will now head to Kensington Palace for a period of rest, said St James's Palace.

The Prince of Wales was all smiles as he boarded the HMS Belfast on an official visit. He also visited the SA Agulhas where he met Sir Ranulph Fiennes and members of The Coldest Journey expedition, a bid to cross the Antarctic in winter

Prince Charles told reporters: “I’m thrilled, marvellous. It’s a very nice thought to become a grandfather in my old age, if I can say so.

“I’m very glad my daughter-in-law is getting better, thank goodness.”

duke and duchess of cambridge

The Duke and Duchess of Cambridge were pictured leaving hospital on Thursday

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."