The Prince of Wales was left in a fit of giggles after catching sight of Prince Harry - immortalised in papier mache.
Charles cried out "Harry" when he was confronted with a row of royal heads, made from old newspapers and wallpaper paste, and pointed to his son - a bright pink ball, with eyes, a nose and a ginger beard and hair made from string.
Charles and wife Camilla came across the art display as they toured the Sandringham Flower Show and were in good spirits, joking and laughing with visitors.
At one point the Duchess playfully patted Charles' bottom a couple of times to encourage him to move along.
And it was a case of "bottoms up" when they enjoyed a pre-lunchtime tipple, sipping pale ale in a garden bar.
The papier mache heads depicting everyone from the Queen and Duke of Edinburgh to the Duke and Duchess of Cambridge, were created by pupils from Flitcham Church of England Primary.
Angela Eden, the school's head teacher, had asked the royal couple if they recognised anyone before the heir to the throne erupted with laughter.
Charles joked: "If you turned it upside down it would look the same with that beard."
Mrs Eden sprang into action and turned the head over and the prince said "no, that's cruel".
The heir to the throne spent a few moments longer chatting to staff from the school and his wife patted his behind to move him along.
The head teacher of the primary near Sandringham, Norfolk said afterwards: "We're a small school, there's only about 70 of us and the younger children worked with the older ones to make the display.
"We wanted to do something that would attract or interest the Royal Family so we decided on the papier mache heads. Prince Harry's my favourite, we all like Harry."