The Prince of Wales and the Duchess of Cornwall sat through a "hairy" mid-air drama when an in flight emergency forced them to land minutes after take-off.
Fifteen minutes out of central London a technical fault forced the royal helicopter to urgently divert to a nearby aerodrome.
Charles and Camilla were flying to Wales on Thursday for a day-long tour to Hay and its popular annual festival of literature.
But minutes after boarding their flight they were urgently diverted to Denham Aerodrome, in Buckinghamshire.
The helicopter, believed to be carrying up to seven people, developed a "technical fault" minutes after take off.
"The pilot carried out a controlled emergency landing after diverting to the airport," a spokesman for the royal couple said.
"It was quite a hairy experience," a source close to the palace added.
Despite the unscheduled stop the royal couple transferred to cars and continued on to the market town of Hay-on-Wye by road.
They finally arrived close to three hours late but emerged looking relaxed and smiling to be greeted by a crowd of several hundred well-wishers.
"They were unflappable despite what they went through. If anyone else had gone through what they did they would have cancelled their day," one pensioner, who preferred not to be named, said.
Neither Charles nor Camilla alluded to their in-flight drama once they arrived at their destination.
An official investigation into the cause of the technical fault is under way.
The lateness of the royal couple's eventual arrival meant that a planned leisurely tour of Hay had to be carried out more quickly.
It started as planned with a quick visit to long-established Hay-on-Wye clothes retailer FW Golesworthy & Sons.
Ethal Pugh, 84, waiting inside the shop, sat on a chair in front of a shoe display hoping, she said, not to be noticed.
Connected to the family which runs the shop, she travelled in from the nearby hamlet of Clifford, in England, and spoke with pride of her 10 grandchildren.
"My daughter said 'mum, you must come,' but I don't want to be a nuisance so I'm sitting here out of the way," she said.
Moments later, she was accosted by the Duchess of Cornwall who, taking her hand and shaking it, said: "Pleased to meet you."
Unprepared for the fleeting glimpse of royalty, Ms Pugh said: "I have no idea at all who that was."
After being told that she had just shaken hands with Camilla, the Duchess of Cornwall, she said: "It was brief, but memorable."