Sharing their delight over the royal baby news on Tuesday, the Duke and Duchess of Cambridge had a laugh as William called Kate an "uncle".
Attending the launch of the inaugral King's Cup regatta at the Cutty Sark, Prince William responded to a question about Baby Sussex, saying:
"Yes absolutely, [I'm an] uncle, second time for me," and then pointed at his wife Kate and added "and you as well."
Kate quickly quipped back "I'm definitely not an uncle", with the pair bursting into fits of laughter.
Prince William continued: "Obviously thrilled, absolutely thrilled, and obviously looking forward to seeing them in the next few days when things have quietened down. I'm very pleased and glad to welcome my own brother into the sleep deprivation society that is parenting."
When asked whether he had any pearls of wisdom for his younger brother, William laughed and remarked: "Plenty of advice, plenty of advice, but no I wish him all the best and I hope the next few days they can settle down and enjoy having a newborn in their family and the joys that come with that."
Kate then added: "It's such a special time, obviously with Louis and Charlotte just having had their birthdays it's such a great time of year to have a baby, spring is in the air." She continued: "As William said, we're looking forward to meeting him and finding out what his name's going to be, so it's really exciting for both of them and we wish them all the best. These next few weeks are always a bit daunting the first time round so we wish them all the best."