The Duke of Edinburgh is said to have spent 15 minutes at a Little Chef in South Yorkshire while en route to a private engagement.
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Prince Philip was recently spotted at a Little Chef roadside restaurant
A witness spoke to the Sun about the "extraordinary" moment a convoy of luxury cars pulled up at the eatery.
"There was massive security and everyone was wondering who on earth had turned up – then we realised it was the duke," the onlooker said.
It is not thought that the Queen's husband, 93, ordered any food while in the restaurant, although members of his team reportedly bought coffee.
Even the Little Chef's £10.99 Royal Breakfast couldn't tempt the royal – "Next time he might go for that," a spokesman for the chain commented.
Philip was on his way to the Lowther Show when he made the pit-stop. He is the patron of the countryside event and has missed only a handful of shows since they began 35 years ago.
The duke joined an estimated 60,000 spectators over the three days at the show, during which he helped to judge the carriage driving competition.