LONDON – The Queen has been filmed saying Chinese officials were "very rude" during last year's state visit by President Xi Jinping.
She was discussing their treatment of Britain's ambassador to China with a senior police officer at a Buckingham Palace garden party on Tuesday.
It came after David Cameron was overheard saying Afghanistan and Nigeria were "fantastically corrupt".
Buckingham Palace said the Chinese visit had been "extremely successful".
The invitation to President Xi was part of the government's policy of courting Chinese investment.
The Queen's remarks were filmed as she was introduced to Metropolitan Police Commander Lucy D'Orsi, who the monarch is told had overseen security during President Xi's visit to the UK in October.
She is heard to respond: "Oh, bad luck."
An official went on to tell the Queen that Commander D'Orsi had been "seriously, seriously undermined by the Chinese, but she managed to hold her own and remain in command".
Commander D'Orsi told the Queen: "I was the Gold Commander so I'm not sure whether you knew, but it was quite a testing time for…"
"I did," the Queen said.
Commander D'Orsi continued: "It was at the point they walked out of Lancaster House and told me that the trip was off, that I felt…"
The Queen said: "They were very rude to the ambassador."
Commander D'Orsi replied: "They were… it was very rude and undiplomatic I thought."
The Queen described it as "extraordinary".
A Buckingham Palace spokesman later said: "We do not comment on the Queen's private conversations.
"However, the Chinese State Visit was extremely successful and all parties worked closely to ensure it proceeded smoothly."
Royal garden parties are filmed by the cameraman who covers the palace for UK broadcasters.
Foreign Secretary Philip Hammond said that "at times it got a bit stressful on both sides" but that state visits were big logistical challenges.
At the palace, Ms D'Orsi told reporters it had been "rewarding" to be thanked by the Queen for her work during the state visit.
She said the Queen and her own mother had chatted about the benefits of being grandmothers.
A Metropolitan Police spokesman has said it was not prepared to discuss a private conversation.