Prince Charles laughed as a well-wisher shouted to him, "Congratulations Sir, it's triplets!"
As the Prince walked over to say hello, John Dowson joked, "I heard it on the radio".
Mr Dowson said afterwards, "He just laughed, he was really jolly. Everybody's so excited in the country for him".
More top news
After the heatwave come the storms, with lightning flashes illuminating the night sky across much of the country last night.
An Independence Day event at a UK base has been cancelled by the US Air Force over security fears.
British firms predict the economy should sustain a "solid" pace of growth for the rest of the year thanks to lower oil prices and inflation.