The Princess of Wales showed off her barista skills during a visit to London Borough Market - but her husband was not as impressed.
Huge crowds formed on Thursday to catch a glimpse of the pair - who even pitched in by serving customers.
Kate made husband William a coffee - only for him to turn it away when he realised it wasn't decaf.
Elsewhere she told a brewer that she had to stay clear of alcohol because of her cancer diagnosis.
The Princess of Wales showed off her barista skills during a stop at Change Please, a social enterprise training homeless people in coffee retail.
She handed the finished drink to her husband, saying "I've made a coffee for you, William", but when he asked "is it decaf?" and she replied "no", he suggested it should be sold.
Kate carried the coffee with her when they carried on with their tour of the popular attraction that has been a focus for food lovers for decades.
Staff member Lorent Maliqi said afterwards: "She did really well.
"I was surprised, she got the texture of the milk right on point - it was a great effort."
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William and Kate were hands-on throughout their visit, which began at the Trethowan Brothers stall where award-winning cheese made from their farm in north Somerset has been sold since the early days of Borough Market almost 30 years ago.
They went on to sample some handmade Pitchfork Cheddar, made with unpasteurised milk, and the Gorwydd Caerphilly cheese, and told Todd Trethowan: "That's lunch taken care of."
They then moved behind the counter, cutting a wedge of Caerphilly cheese under Mr Trethowan's guidance, before Kate used the wire to slice some of the cheddar, which was bagged and handed to the couple's aide for later.
Dozens of onlookers packed out the busy central London market to get pictures of the pair.
The pair then spoke to Kim Innes, who runs Humble Crumble, as she dished out servings of crumble to customers.
"They were really keen to do it and really good at it, and they put on aprons and everything," Ms Innes said.
"They were both encouraging each other and were complimentary about each other's work."
Earlier in the day, the pair were declared winners in a pint pulling contest against the founder of a brewery, as they visited London's Bermondsey Beer Mile.
They were invited to try beers and ciders at the Fabal Beerhall, and went behind the bar at the Southwark Brewing Company.
Kate asked brewer Hannah Rhodes if they had any non-alcoholic beers, saying she had to stay clear of alcohol since her cancer diagnosis.
"She said something along the lines of 'since my diagnosis it has been best to avoid alcohol'," Ms Rhodes told the Press Association.
(c) Sky News 2026: Prince William turns down Kate's coffee - because it wasn't decaf
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