The Princess of Wales was snapped giving David Beckham a peck on the cheek at Prince William's glamourous Earthshot Award ceremony in Boston on Friday night.
Kate, 40, looked delighted to welcome the football superstar, who was a surprise guest at the environmental awareness event.
The Prince and Princess of Wales were met with rapturous applause when they arrived at the gala, with Kate draped in an off-the-shoulder green dress by Solace London, which she rented for between $91 (£74) and $238 (£194), according to the Daily Mail.
Kate paired the dress with a stunning art deco choker reported to be worth more than $15 million.
The piece was gifted to Diana by the late Queen, who inherited from her grandmother Queen Mary.
The winners of the £1 million awards were Indian 'Greenhouse-in-a-Box' startup Kyeti, Kenya's Mukuru Clean Stoves, Indigenous Women of the Great Barrier Reef, plastic reduction group NOTPLA and Fix Our Climate.
All attendees arrived in hybrid vehicles in keeping with the environmental theme.
Other celerbrity guests included singer Billie Eilish who performed at the event along with Ellie Goulding, Finneas and Annie Lennox.
Presenters of the award included radio broadcaster Clara Amfo, actor Rami Malek, and environmentalist Sir David Attenborough.
Also in attendance were Earthshot council members John Kerry, Ms Naomi Yamazaki, Hindou Ibrahim and Indra Nooyi, as well as the program's CEO Hannah Jones.
During the event, Elizabeth Solomon, a member of the Massachusetts tribe at Ponkapoag, spoke about indigenous heritage during her opening speech.
"We are gathered today in Native space and on the traditional lands of the Massachusetts Tribe," she said.
"Please treat our lands and waters as precious because they are. 10,000 years ago Boston Harbor was dry land and we were here. 1,000 years ago much of what is now known as the city of Boston was not land but water and we were here. 400 years ago colonists came to occupy our land and we were here."
Prince William delivered the closing speech at the event.
“I believe that the Earthshot solutions you have seen this evening prove we can overcome our planet’s greatest challenges," he said.
"And by supporting and scaling them we can change our future. Alongside tonight’s winners and finalists, and those to be discovered over the years to come, it’s my hope the Earthshot legacy will continue to grow, helping our communities and our planet to thrive.”
The Earthshot Prize aims to "discover and help scale innovative solutions that put the world firmly on a trajectory toward a stable climate by 2030" and "build a world in which communities, oceans and biodiversity can thrive in harmony".
