Prince William and Kate Middleton have sweet reunion with wedding singer Ellie Goulding at Earthshot Prize ceremony

Catherine, Princess of Wales, and Prince William had a sweet reunion with someone who played a key role in their fairytale wedding over a decade ago – singer Ellie Goulding.

Goulding, 35, performed her version of Elton John's Your Song at the royal couple's 2011 wedding reception, and she was also a performer at William's Earthshot Prize Awards ceremony in Boston.

After the show, the Waleses, both 40, spoke with some of the performers backstage, with images showing them excitedly chatting with Goulding, whose wedding performance was actually the soundtrack to the Prince and Princess of Wales' first dance.

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William and Catherine were also seen mingling with celebrities David Beckham, Rami Malek and Chloe and Halle Bailey at the event, which was held on Friday night local time.

The royal couple's appearance at the Earthshot Prize Awards ceremony officially concluded their three-day visit to the United States, which has been marred by fresh accusations of racism back at Buckingham Palace, as well as the release of Prince Harry and Meghan Markle's Netflix docuseries trailer.

At the event, Catherine adhered to the sustainable fashion guidelines – guests were asked not to purchase new outfits for the earth-friendly evening – wearing a bright green off-the-shoulder by Solace London, which she rented for £74 (approx. $134) from UK designer rental platform HURR.

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Notably, Catherine's accessories were also recycled – and one in particular honoured her late mother-in-law. On Catherine's neck sat Princess Diana's Art Deco emerald and diamond choker, which the former of Princess of Wales notably wore as a headband on a visit to Australia.

The choker was made for Queen Mary by Garrard in 1921 from emeralds gifted by the Ladies of India in 1911. It is part of a larger parure of emerald and diamond pieces, which were inherited by the late Queen Elizabeth II.

Her Majesty gave Diana the choker on a long-term loan and the former Princess of Wales wore it many times during her life

Catherine also wore halo emerald and diamond earrings by Asprey, which are mounted in platinum. William opted for a blue velvet blazer, which he has worn to past royal events.

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William also spoke at the event, where he presented five winners from across the Earthshot Prize's five categories with awards, which include £1 million (approx. $1.8 million) in grants each, which the winners are to put towards their project's goals.

"When I founded this Prize in 2020, it was with the ambition to harness the same spirit of ingenuity that inspired President John F. Kennedy to challenge the American people to put a person on the moon within a decade," William said, according to the Daily Mail's royal editor Rebecca English.

"So, it has been an honour to share the stories of our Earthshot winners and finalists from the heart of his hometown."

"I believe that the Earthshot solutions you have seen this evening prove we can overcome our planet's greatest challenges, and by supporting and scaling them, we can change our future," he continued, expressing his "hope" that the Earthshot legacy will only grow in future.

"The decisions we make now will affect generations to come," he said. "Which is why we must choose the path of hope, optimism, and urgency to repair our planet."

The winners, which William announced on the night, are Mukuru Clean Stoves from Kenya, Kheyti from India, Notpla from the United Kingdom and 44.01 from Oman.

Notably, the Queensland Indigenous Women Ranger Network of the Great Barrier Reef from Australia also won the prize for the Ocean category.