Kate Middleton and Prince William Sit Courtside for Boston Celtics Game: "Let's Go!"

William's Earthshot Prize Awards event on Friday brought the Prince and Princess of Wales to Boston on Wednesday for a three-day visit.

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Kate Middleton and Prince William visited one of Boston's favorite sports teams on their first day in the U.S.

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The Prince and Princess of Wales unexpectedly attended the Boston Celtics-Miami Heat game at the TD Garden on Wednesday night.

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The sports-loving pair sat courtside with former NBA player and Massachusetts Governor-Elect Maura Healey, Celtics great Thomas "Satch" Sanders, and the team's two main owners and their wives.

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The Celtics prevailed while Kate and William spoke with their neighbors and clapped loudly.

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William and Kate, both 40, shared a behind-the-scenes photo of the Celtics warming up before the game. "Let's go Celtics!" they wrote.

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The couple landed in Boston on Wednesday for the second Earthshot Prize Awards event on Friday. The basketball game referenced Earthshot's entrance in the city.

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The Celtics honored a 15-year-old climate activist during their "Hero Among Us" tradition. William and Kate chatted with the teen during a break.

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The pair met Celtics family members, including officials of the Boston Celtics Shamrock Foundation, which provides grassroots programming and strategic support to local at-risk organizations.

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Kate was interested in the "Curbside Care" mobile unit, which will work with Boston Medical Center to deliver comprehensive, streamlined care to women and newborns in the first six weeks of life at patient doorsteps.

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