Kate Middleton is the wife of Prince William, 38, and a senior working royal. In this role she regularly joins other members of the family at official events.
Most years, members of the Royal Family will flock to Sandringham for a church service with the Queen.
While the coronavirus meant this could not happen in 2020, Kate has been a regular at the services since she married Prince William in 2011.
Royal fans will often head to the church to catch a glimpse of the royals and members of the family will take time to greet wellwishers.
Kate appeared amused at a comment from one royal fan outside the church in 2018 and some are still curious to what their conversation was.
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Sharing pictures from the exchange on Twitter, a social media user wrote: “I’ve always wanted to know what this lady said to Catherine.”
The picture showed Kate looking into the distance with a slightly embarrassed smile on her face while speaking to one woman.
Body language expert Judi James commented on the exchange to suggest the topic of their conversation was a humorous one.
Speaking to Express.co.uk, she stated: “Kate isn’t known for her comedy facial expressions, which is why this dimpled mouth-clamp is so cute.
“We’ll have to guess exactly what prompted it but overall it looks like an expression of mock-embarrassment and it is totally complimentary to the open-mouth, ‘prompting’ laugh and eye-gaze of the woman she is talking to.
“Their body language does provide some clues about their conversation. Kate is still leaning into towards the woman, showing she’s sharing the fun rather than reeling back in genuine embarrassment.
“Her smile is a self-effacing one, with the lips pulled inward, and her eye-gaze is directed away from the woman, either towards William or just averted to a reflective space.”
The body language of both women suggested something has been said to make Kate show playful embarrassment, Judi continued.
She explained: “The way the woman looks up into Kate’s face with that gloriously large smile suggests she’s stoking the humour here. She has one hand holding her phone out to suggest a selfie but the back of the other hand is tapping Kate’s hand, suggesting a collusion signal as though she’s being a bit cheeky.
“This could easily be a cheeky comment about William but I do wonder if Kate would be quite so full-on funny when she is more likely to be respectful about her husband unless he is in earshot and able to join in the banter.
“It might be equally non-Kate for the duchess to pull a face like this if the woman was referring to their matching coloured coats as it could have looked rude.”
Analysing the photo, Judi claimed the embarrassment may also have come from Kate getting something wrong, prompting the fan to tell her off in a joking way.
Whatever the conversation, the expert suggested Kate took the conversation in good spirits.
She added: “We’ve all become a bit befuddled during lockdown and many of us can be frequently heard joking about memory lapses.
“The royals tend to remember regular fans who turn up at events like this and they often know them by name. Did Kate drop the wrong name here?
“It could account for the fact that the woman’s hand-tap could be a method of gently telling her off here, although only in a joking way, of course.”