We all know what can happen when an elegantly attired woman in a figure-hugging dress walks past a group of builders.
But scaffolder Sam Wayne had a nobler aim when the Duchess of Cambridge strolled past with her husband - he just wanted to add to his collection of selfies with Royals.
Having taken a picture of himself with the Prince of Wales two years ago, he decided it was too good an opportunity to miss yesterday when Kate and William visited the site in Cornwall where he is working.
As the couple walked past a line of builders in hard hats, Mr Wayne, 36, stepped forward and got out his mobile phone ready to take a snap from several metres away.
Spotting him, smiling William joked: "That's got to be a bad selfie."
Afterwards, Mr Wayne, a married father of one, from Redruth, said: "I was told no selfies before the visit, but I took one.
"It was more in the distance than with Prince Charles, but it came out clear enough. When William said it would be terrible, I said, 'I had one with your dad' hoping he would stop and I could do one closer but they kept on walking.
"I'm a bit of a selfie freak, I suppose. I was in the right place at the right time - or the right place at the wrong time, depending how you look at it."
The Duchess, wearing a blush pink dress by US designer Lela Rose and a pair of nude wedges from Monsoon, appeared amused by Mr Wayne's antics.
The scaffolder posted two selfies with the couple in the background on his Facebook page along with the message: "He's done it again. Prince William and Kate Middleton not as close as my Prince Charles but still a royal selfie."
The Prince of Wales posed with Mr Wayne in 2014 during a visit to an affordable housing project in Newquay.
On that occasion, Mr Wayne asked for a picture - and the heir to the throne agreed. Kate and William, on their first official visit to the Duchy of Cornwall, were at the Nansledan development in Newquay, a 'model town' similar to the Prince of Wales's Poundbury estate in Devon.
Built by the Duchy, it is intended to provide sustainable housing, with 4,000 jobs being created for its 4,000 households.
Earlier, on the first day of their two-day tour of Cornwall, Kate pulled a pint of Rattler cider when the couple visited Healeys Cyder Farm, Penhallow, near Truro.
Also in Truro, where they showed support for a £3.2 million campaign to raise cash for a new slate roof for the cathedral, William accepted a kiss from retired teaching assistant Linda Moore, 62. "I said, 'can I give you a kiss?' and he said, 'You can give me peck on the cheek,' Mrs Moore revealed. "And when Kate came over he said about me: 'Watch that woman'."
The royal couple, with an entourage of six, were due to spend last night at Restormel Manor, a 500-year-old nine-bedroom manor house in Lostwithiel, Cornwall, owned by the Duchy of Cornwall.