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The Duchess of Cambridge did not just sit quietly and pose for her beautiful 40th birthday portraits. Instead, fashion photographer Paolo Roversi, who was tasked with photographing Kate, said he persuaded her to dance an "accelerated waltz mixed with a pinch of rock 'n roll" in the white Alexander McQueen dress she wore.
Reversi said it reminded him of a classical ballerina, and despite the Duchess's initial nerves, "in the end I wanted to take pictures in motion, so with that wonderful wide skirt I made her dance in front of my lens."
He admitted: "Every day she is machine-gunned by photographers but not used to posing; knowing my photos with the models she was a bit fearful in facing a real session, which then required about four hours of work. But once she started it would be very easy, I reassured her."
Kate is not a stranger to dancing, however. On several occasions, the sport-loving royal, who keeps in shape with yoga, running and weights, has been required to dance on duty - once, with a life-sized Paddington.
She's not the only royal who has taken to the floor. In fact, she joins a long line of regal movers, including her late mother-in-law, Princess Diana.
Diana was known for her love of dancing, and famously, danced on stage with ballet star Wayne Sleep, as a surprise for Charles. The pair danced to Billy Joel's Uptown Girl, and the moment was replayed in season four of The Crown, in scenes suggesting that the Prince was more embarrassed than delighted.
Sleep later explained, "There was a gasp from the audience, of 2,500 people, who took an intake of breath all at the same time. They were speechless."
Of their rehearsals, he said, "She was in leg-warmers and a leotard. My first thought was, she's too tall to dance with me, I'll be a laughing stock: I'm 5ft 2in and she's 5ft 11in.
"But I soon realised she had a good sense of humour, and that we could have some fun with our height difference. She'd already decided on the music: Billy Joel's Uptown Girl."
He also said, "There was a music video that went with the song and she must've seen the video. There's a lovely lady with a hat—she's very chic and gets out of a car. Diana knew she could play that role of sophistication."
Vanity Fair's editor, Tina Brown, later wrote, "It was embarrassingly clear that he had not been ravished by the spectacle of his wife en pointe. His disappointing response, when it leaked, was interpreted as frigid disapproval of Diana's lapse in royal etiquette."
However, the same year, dance-loving Diana, who had been a ballet student and loved roller-disco, also danced with John Travolta at The White House, watched by the Reagans.
And back in 1983, she made headlines dancing with Charles on their official tour of Australia, when she wore a diamond and emerald necklace given to her by the Queen as a headband.
Previous generations of royals were expected to learn to dance as part of their duties - from coming-out debutante balls to state receptions, ballroom dancing to a competent level was considered a necessary skill.
The Queen and her late sister Princess Margaret learned to dance as children, at Vacani's School of Dance. The school, opened in 1915, is still going.
The website explains, "the young Earl of Harewood’s attendance at the school led to an invitation from the future Queen Mother to give private classes to the young Princesses Elizabeth and Margaret Rose.
"Every week during the war, Betty Vacani and her aunt would visit Kensington Palace, and later Windsor Castle to teach the princesses and other children of the royal household.
"Later, Prince Charles apparently excelled at the Highland Fling. In the late 1970s, Lady Diana Spencer studied ballet and briefly taught at the Vacani school."
But while Princess Elizabeth has only ever danced formally in public, on the arm of Prince Philip, and various Kings and presidents, her younger sister, Princess Margaret, was known to love a good dance, whether it was jiving to rock n' roll or grooving to reggae.
Her former Lady in Waiting and best friend, Anne Glenconner, recalled, "tI hink some of the happiest times she had (were in Mustique), the people of the Caribbean loved her.
"They called her 'our Princess' and she loved dancing to reggae bands. We had a really good time."
While Prince Charles is not known for his love of dancing - beyond the Highland Fling - the Duchess of Cornwall seemingly enjoys getting up and joining in, as she's proved on various royal tours over the years.
Even The Duchess of Sussex, whose entry into royal life didn't last long, looked overjoyed to be dancing with young children in Africa on her first royal tour.
Every royal knows that at some point, they'll be required to hit the dance floor, whether it's gamely engaging with a traditional folk dance, or formally waltzing with a president.
Luckily, so far, few have put a foot wrong.
Watch: How Kate Middleton paid tribute to Princess Diana in her 40th birthday portrait