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After a St. Patrick's Day toast back home, Kate Middleton and Prince William jetted off to Paris Friday, marking his first official royal visit to the city since his mother Princess Diana died there 20 years ago.

The Duchess of Cambridge wore a custom double-breasted emerald green Catherine Walker dress coat, the same one she sported earlier in the day when she and William attended the annual Irish Guards St Patrick's Day Parade at Household Cavalry Barracks in London, but let her hair down and appeared to leave her fascinator hat behind.

The two traveled to Paris by request of the Foreign and Commonwealth Office and headed straight to the Elysee Palace, where they met with French President Francois Hollande.

Prince William, Francois Hollande, Kate Middleton, Paris

Chris Jackson/Getty Images

Princess Diana, Prince William, 1983

Jayne Fincher/Princess Diana Archive/Getty Images

Diana, one of the most beloved royals in the world, died in a car crash in the French capital in 1997 after being chased by paparazzi. She was 36.

William has traveled to the city since her death but not for an official royal visit. In 2007, he and brother Prince Harry attended the Rugby World Cup final in the suburb of Saint-Denis and later partied with England players at an after-party at the L'Etoile nightclub, near the Paris landmark the Arc de Triomphe.

Kate Middleton, Catherine, Duchess of Cambridge, Paris

Mirrorpix/Splash News

The Duchess of Cambridge later changed into an elegant, sleeveless, long black Alexander McQueen dress and accompanied William to a reception to mark the launch of the program Les Voisins ["The Neighbors"], hosted by Britain's ambassador to France, Edward Llewellyn, at the British Embassy in Paris. There, they met French leaders from the arts, business, fashion, sport and voluntary sectors, as well as military award winners.

"Like all neighbors, sometimes our two nations encourage each other through mutual support," William said in a speech. "Sometimes we attempt to outdo the other through rivalry—as we will see tomorrow when Wales play France at the rugby. But always our two nations continually inspire one another to become better: more creative, more prosperous, more innovative."

"This partnership will continue despite Britain's recent decision to leave the European Union," he added. "The depth of our friendship and the breadth of our cooperation will not change."

William also said that before they arrived, his grandmother Queen Elizabeth II reminded him of how much she has enjoyed her many visits to France.

"It is a feeling that Catherine and I entirely share, and look forward to this and many more visits in the years to come—to France our ally, our friend, our neighbor," he said.

During their visit, the royal couple is also set to meet soccer player Robert Pires and actors Jean Reno, Kristin Scott-Thomas, and Audrey Tautou.

Earlier Friday, after the parade of the Irish Guards, Kate and William knocked back pints of Guinness to celebrate the holiday and met soldiers and their families for lunch in the welfare center of the barracks.

The couple's appearances came after William embarked on a boys-only ski trip to Verbier, Switzerland, where he was caught on video "dad dancing" while partying with friends at a nightclub. A source told E! News Thursday that Kate is "disappointed" in his behavior.