The Prince of Wales has told environmental campaigners their cause was close to his grandmother's heart - and that their support for it was giving him "great comfort".
In a personal message recorded a day after the Queen's funeral, and broadcast on Wednesday, William told those gathered in New York for the Earthshot Prize innovation summit, it was "the saddest of circumstances" that had prevented him from joining them.
But he told them: "Protecting the environment was a cause close to my grandmother's heart, and I know she would have been delighted to hear about this event and the support you are all giving our Earthshot Finalists - the next generation of environmental pioneers.
"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 Prince of Wales has often spoken about his relationship with the Queen.
In a moving tribute following her death, he said she had always been by his side "during the saddest days of my life" and that the reality of "life without granny" would take some time to sink in.
Cause for optimism
He first came up with the idea of the Earthshot Prize in 2018.
He said, at the time, there was too much pessimism in the climate debate, and that he wanted to inject some optimism.
The contest is inspired by JFK's Moonshot Project, and hopes to inspire environmentally conscious innovators of the future.
Over the next decade, £5m in prizes will be awarded every year to the best ideas.
He told this year's Prize 'summit' meeting via the video message that he knew the world was in "an uncertain place right now" and that many families and communities were facing "unimaginable challenges - from conflict to energy crises and food shortages".
But he added: "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."
The finalists for the 2022 prize will be announced in the coming weeks, and their ideas, the Prince said, gave him cause for great optimism.
"These pioneers exemplify the leadership needed in this decade of change."
But he warned it should be a joint, global effort.
"We must come together behind their innovative solutions to ensure they reach their full potential with pace and scale," he said.
"We must collaborate in new ways, and we must be courageous.
"And as the Moonshot inspired a great decade of technological transformation, our Earthshot decade must inspire action, creativity and collaboration around the globe.
"Together, we need to ensure the transition to sustainable solutions is the fastest and most endemic change the world has ever known."