Kate Middleton appears to have referred to Prince Charles as "grandpa" during a meeting at the G7 summit.
A lipreader told CornwallLive that the Duchess of Cambridge had used the moniker for her father-in-law at the Eden Project.
Kate, Charles, the Queen, Prince William and Camilla, Duchess of Cornwall, all arrived at the eco-visitor attraction on Friday.
The royals were attending a drinks reception with some of the world's leaders, who were in Cornwall for the political summit.
And it appears that, upon arrival, Kate said to Charles: "Hello Grandpa, how are you?"
The future king of England is grandfather to Kate and William's three children, George, Charlotte and Louis.
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The lipreader also revealed some of the royals' other comments as they walked through part of the project.
It is thought Camilla said she was holding the Queen's "shawl" during one conversation.
The lipreader said the pair shared a sweet moment, as Camilla asked the Queen if she would like to wear the garment.
The Queen, Prince Charles and Camilla were approaching a corner of the venue as Charles looked on towards both of them.
According to the lip reader, Camilla then asks the Queen if she would like her scarf.
Camilla appeared to hold the shawl out, saying: "Here is your shawl."
The Queen then said: "You have it."
To which Camilla replied: "Are you sure?"
And Charles added: "She doesn’t want it."
The event saw the royals mingle with political figures including US president Joe Biden and German chancellor Angela Merkel.
And it came on the same day as an engagement which saw the Queen insist on borrowing a sword - to cut a cake.
The monarch had been handed the sword by Edward Bolitho, the Lord-Lieutenant of Cornwall, at the Big Lunch.
When told by an aide that there was a conventional knife available, the Queen replied: "I know there is, this is more unusual".
The Duchess of Cornwall commented: "That's slicing through" before assisting with the final part of cutting the cake.
After handing the ceremonial sword back, the Queen used a knife to cut a second slice of cake and remarked: "That looks very good".
The G7 summit took place in Carbis Bay this weekend, where world leaders gathered to discuss important events.
The dinner attended by the royals marked the first time the family had been seen in public together since the birth of Lilibet, the daughter of Prince Harry and Meghan Markle.
