Prince William has released a video message for the Earthshot Prize innovation summit, recorded just a day after Queen Elizabeth II's funeral.
The Prince of Wales, as he is now titled, had been due to travel to New York to attend the summit ahead of the awards being staged in the US in December.
It comes as a number of royals get set to return to their duties, despite the family observing a official period of mourning for the deceased monarch.
Flags at royal residences will remain at half-mast until 8am on Tuesday – the final day of royal mourning.
King Charles has not had any engagements since the funeral, where he was visibly emotional after an intense period in which he grieved for his mother, visited all four nations of the UK, and became monarch.
Queen Elizabeth II's only daughter, Princess Anne, will on Thursday meet Royal Navy personnel who took part in the funeral procession for the queen, while the queen's youngest son Prince Edward will visit Estonia and Germany to meet troops on a three-day trip.
Prince William had been scheduled to make the solo trip to the US on Wednesday, where he would have been joined by previous winners of his £50 million global environmental competition.
In a video recorded on Tuesday at the Windsor Estate and broadcast on Wednesday, the prince said he believed the queen would have “been delighted to hear about” the summit.
Addressing those gathered in New York for the event, Prince William said: “Though it is the saddest of circumstances that means I cannot join you in person today, I am pleased to be able to join you in video form as you gather in New York for the Earthshot Prize innovation summit.”
He added: “During this time of grief, I take great comfort in your continued enthusiasm, optimism and commitment to the Earthshot Prize and what we are trying to achieve.
The Earthshot Prize was founded by Prince William and his Royal Foundation in 2020, and in July this year the project became an independent charity, with the prince as its president.
The second Earthshot Prize awards ceremony is set to be held in Boston in December, after the inaugural event at London’s Alexandra Palace last year.
Prince William said both he and the Princess of Wales are “so excited” to travel to Boston.
He last visited the US in 2014 when he travelled to New York with his wife Kate, who was then pregnant with Princess Charlotte, for a three-day tour.
Prince William acknowledged in his message that the world is “an uncertain place right now”, noting that many people “are facing unimaginable challenges – from conflict to energy crises and food shortages”.
He said: “While addressing these in the short term, we must also remain resolutely focused on tackling the greatest challenges that threaten our tomorrow.
“Because if we don’t, the changing climate will only serve to entrench these immediate challenges into fundamental global issues, severely impacting the lives of each and every one of us. That is why our collective mission is so urgent.”
But striking a more optimistic tone, Prince William insisted that “we can protect our world for our children, our grandchildren and the generations that will follow them”, citing last year’s cohort of Earthshot winners and finalists, who he described as “inspiring activists” and “brilliant innovators”.
Prince William said the Earthshot decade “must inspire action, creativity and collaboration around the globe” and called on people to “ensure the transition to sustainable solutions is the fastest and most endemic change the world has ever known”.