Prince William wants to sign up to the gym.
The 35-year-old royal is said to be keen to sign up with the Chelsea Harbour Club, the exclusive gym his mother, the late Princess Diana of Wales, used to go to.
It is believed he stopped off there after dropping his son Prince George, four, to school at Thomas's Battersea one day.
A source told the Daily Mail newspaper of his visit: "He visited the cafe and told staff that Diana would buy a cookie for him as a treat if he'd been behaving well. He still remembers how special they were. The chefs started flapping, saying they'd find the recipe and rustle one up right away, but he said he didn't want any special treatment."
However, the Duke of Cambridge may find it difficult to make time to go to the gym after the couple - who are also parents to two-year-old daughter Princess Charlotte - recently revealed they are expecting their third child.
A statement from Kensington Palace read: "Their Royal Highnesses the Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting their third child. The Queen and both their families are delighted with the news.
"As with her previous two pregnancies, the Duchess is suffering from Hyperemisis Gravidarum. Her Royal Highness will no longer carry out her planned engagement at the Hornsey Road Children's Centre in London today. The Duchess is being cared for at Kensington Palace."