Prince William had a priceless reaction after being hit with a cheeky comment about his physique and wife Kate, the Princess of Wales.
It came as he visited the Oak Cancer Centre - a brand new £70million treatment and research centre - in Sutton, which is part of the Royal Marsden NHS Trust.
William is president of the Royal Marsden and was on hand to officially open the new building as well as meet some of the patients and staff.
There, he met one man, who had been treated for cancer, as well as his wife and he shook both their hands.
And the man couldn't resist making a cheeky comment for the future King and told him: "You're a tall b****r, aren't you?"
It left William and everybody else gathered in stitches and he jokingly replied: "I'm wearing heels."
The man's wife then went on to tell William how grateful she was for the treatment her husband had received but he was not finished joking with the prince.
He then told him: "And your wife is not bad, she's a nice lady as well."
William laughed and remarked: "He's a chatty one... every nurse has got an eye on you."
Elsewhere on the visit, William was reunited with Matron Lorraine Hyde, who he had first met while on work experience with the Royal Marsden Trust.
Shaking her hand, he said: "I remember, it was about 18 years ago when I was here doing my work experience in those good old uni days."
Meanwhile, laughing with another patient, he reassured them that cancer had "picked the wrong person to mess with".
Emma Bishop, 38, was diagnosed with stage four lung cancer last year. Thanks to groundbreaking treatment at the hospital, the mother-of-two was able to run the London marathon for the Royal Marsden Cancer Charity and raised £100,000.
She said: "I was dying and we were terrified. The Royal Marsden and my super prof [her doctor, Sanjay Popat] have saved my life.
"Cancer treatment gives you time, time is quite simply the most precious resource we have."
She added that the new centre will give patients hope which is "the greatest gift".
As the prince was preparing to leave, a group of children from the staff nursery onsite gathered to wave him off wearing paper crowns and holding a banner reading "Welcome Prince William".
The prince couldn't resist going over to say hello, complimenting one young girl on her strawberry dress.
William has been president of the Royal Marsden since 2007, with the position previously held by his mother, Princess Diana.
The new centre, funded by the Royal Marsden Cancer Charity, places researchers and patients under the same roof, to accelerate the development of new treatments and help diagnose more cancers at an earlier stage.
The prince has been involved in the project from the start and in October 2020 he laid the foundation stone for the new building.
