Prince William's Earthshot Prize really went all in on the "green" theme.

The environmental prize, founded by the Duke of Cambridge, held its first-ever awards ceremony today in London at the Alexandra Palace. The event had a literal green carpet and William sported a one-of-a-kind green velvet jacket for the occasion.

Photos: William and Kate at Earthshot Prize ceremony

While her husband was styled in green, Duchess Kate went with a beautiful lilac or perhaps pale-blue dress. But it was environmentally friendly in its own way, too.

Prince William And Duchess Kate At The Earthshot Prize Award Show

It's been uncovered that Kate's dress is a custom Alexander McQueen that she also wore to the BAFTAs in 2011. As a "recycled" dress, it's a perfect fit for the environmentalist theme.

Stars who also appeared at the ceremony include the British actresses Emma Watson and Emma Thompson.

The Duke and Duchess of Cambridge are hosting the event for The Earthshot Prize, the environmentalist award Prince William founded in 2020.

Prince William And Duchess Kate At The Earthshot Prize Award Show

For the next 10 years, the prize will annually recognize five winners who are creating solutions to address pressing environmental issues. The goal is to incentivize researchers to "repair our planet" for future generations.

Fifteen finalists for the inaugural Earthshot Prize were announced in September, and the five winners are being revealed at today's ceremony.

It also marks another red — check that, green — carpet appearance by the royals, who attended the No Time to Die premiere last month.

Prince William is also in an ongoing environmental dialogue with William Shatner after the royal criticized the recent trend of the exceedingly wealthy venturing off into space.