The Duke and Duchess of Cambridge were photographed attending the first ever Earthshot Prize awards ceremony at Alexandra Palace in London on Sunday.
Organised by Prince William and The Royal Foundation, the prize is designed to find inspiring and innovative solutions to environmental challenges from around the world.
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A star-studded crowd of performers and presenters will join the royals and the prize winners to celebrate.
Ed Sheeran, Coldplay, and Shawn Mendes will be among those performing, and the event will be introduced by Prince William.
The five winners of The Earthshot Prize, each of whom will receive £1million towards their initiative, will be announced by a line-up of presenters which includes The Duchess of Cambridge, Emma Watson and Emma Thompson.
Speaking ahead of the ceremony, Prince Charles said: "I am very proud of my son William for his growing commitment to the environment and the bold ambition of the Earthshot Prize."
Dame Emma Thompson, one of the celebrity presenters, looked laid back but smart in a blue suit and white trainers.
Speaking to the press on the Earthshot Prize’s green carpet, she said her parents would have been horrified by how society now dumps its waste on the streets.
The actress said: "It’s all about thinking differently, it is also about remembering how we used to live - We never used to live like this. We’ve only been mad for about 60 years."
WATCH: The Duke and Duchess of Cambridge arrive for the 2021 Earthshot prize
Dermot O'Leary and Clara Amfo posed on the green carpet ahead of presenting the awards ceremony.
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Speaking about the Duke of Cambridge, Dermot said: "He is so disarming. He is doing an incredible job. It is easy not to stick hid his head above the parapet but he is."
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Harry Potter and Little Women actress Emma Watson was among the stars at the prestigious event, and she looked stunning in an upscaled wedding dress made from 10 dresses from Oxfam.
Guests were asked by organisers to "consider the environment" when choosing their outfits.
The Duchess' gown was a beautiful Alexander McQueen Grecian-style dress from 2011, in keeping with the event's environmentally-conscious theme.
The Earthshot Prize's inaugural 15 finalists include a 14-year-old girl from India who has designed a solar-powered ironing cart, the government of Costa Rica, which has pioneered a project paying local citizens to restore natural ecosystems, and a Chinese app that allows its citizens to hold polluters to account.
Liverpool and Egypt footballer Mo Salah looked sharp on the green carpet, ahead of presenting one of the awards.
Olympian Matthew Pinsent and his wife Demetra were also in attendance for the big event.
YouTube rapper KSI posed on the green carpet ahead of his performance.
During the ceremony, in a short film recorded in the London Eye, Prince William said: "We are alive in the most consequential time in human history… The actions we choose or choose not to take in the next ten years will determine the fate of the planet for the next thousand.
"A decade doesn’t seem long, but humankind has an outstanding record of being able to solve the unsolvable.
"Many of the answers are already out there… but we need everyone – from all parts of society - to raise their ambition and unite in repairing our planet.
"The future is ours to determine. And if we set our minds to it, nothing is impossible."
Actors and married couple David Oyelowo and Jessica Oyelowo were among the stars in attendance.
Prince William addressed attendees on the green carpet ahead of the ceremony.
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Emma Thompson also posed with Nigerian singer Yemi Alade.
Mayor of London Sadiq Khan attended with his wife Saadiya.
Former Conservative Party leader and chair of the Royal Foundation William Hague and his wife Ffion were among the high-profile arrivals.
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