The monarch had received the sword from Edward Bolitho, Lord Lieutenant of Cornwall, for the task of cutting a large cake marking the Great Luncheon at the Eden Project.
When an assistant told her that there was a conventional knife available, the Queen replied: “I know there is, it is more unusual”.
The Duchess of Cornwall commented: ‘It’s deciding’ before helping with the final part of the cake cutting, which was cheered by attendees at the event.
After returning the ceremonial sword, the queen used a knife to cut a second slice of cake and said, “It looks very good. “
Peter Stewart, executive director of Eden Project, introduced the three royals to some 20 guests who had been invited to the event.
“It’s like comets – they don’t come very often,” said Mr. Stewart.
“I was trying to remember the last time the three were on an official engagement together like this. I can only think of one at Fortnum and Mason but that was something else.
“The important thing for me was that there was every reason not to do it.
“The fact that they felt that with the eyes of the G7 there was an opportunity – with the risk of missing trains and everything – to be able to listen to some of the heartfelt stories of the people here.
“It was absolutely priceless. “
Previously, the Queen had hosted an outdoor reception at the Eden Project and was joined by the Prince of Wales, the Duchess of Cornwall and the Duke and Duchess of Cambridge.
Executives including German Chancellor Angela Merkel, as well as Canadian Prime Minister Justin Trudeau and US President Joe Biden, were pictured chatting with the royal family.
The Queen spoke to people at the Big Lunch event, which was held outside in an area separate from Project Eden, about meeting world leaders face to face after a year of restrictions due to the pandemic of Covid-19.
Mr Stewart described how the monarch discussed “communicating on Zoom and so on” due to the coronavirus.
“She was talking about the fact that she usually meets world leaders and has not met them for two years and she brought it down to the importance of everyday life and getting to know our neighbors”, a- he added.
The Grand Déjeuner is an annual gathering for neighbors and communities, with people encouraged to share friendship, food and to get to know each other better.
It has been in operation since 2009 and is an idea of Project Eden, supported by the National Lottery.
The Duchess of Cornwall is the event’s godmother and celebrated her 10th birthday with a luncheon at the Eden Project in 2019.
For the past two years it has been operating online due to Covid-19, but next year it will officially be part of the Queen’s Platinum Jubilee celebrations.
Mr Stewart paid tribute to the guests who attended Friday’s engagement, who had been nominated for their services, especially during the pandemic.
“There was a time when Her Majesty was talking to a lady called Irene Rowe, who was a caregiver for 20 years and caught Covid and recovered and returned to work,” he said.
“She came home and gave Covid to her husband, who sadly passed away. She asked Her Majesty how she was doing and offered her condolences for the loss of her own husband, The Duke of Edinburgh.
Ms Rowe, 65, of Helston, spoke to the Queen and Kate about the death of her husband Malcolm, 62, in February this year.
After informing the Queen of her loss, she was asked how she was doing.
“I said you were the same – you just carried on like I did,” said Ms Rowe, a grandmother of eight.
“I said you had to keep going. I have a good job, friends and family. The people were very nice.
“Kate touched my arm when I told her about my husband and said ‘oh no’.
“She was really caring and very kind, they both were.
“She asked if we could see him at the hospital and I said we couldn’t, we weren’t allowed to. “
At the end of the event, the Queen, Camilla, and Kate left in separate vehicles.