Prince William wears 20-year-old trousers to Earthshot Prize Awards

While the Duchess of Cambridge may have stolen the show by re-wearing a 10-year-old Alexander McQueen gown to the Earthshot Prize Awards, Prince William was also doing his part to go green.

The Duke of Cambridge wore a pair of pants that were 20 years old, beating his wife's own look in terms of age.

He paired the slacks with a green velvet blazer first worn to an event for homeless charity Centrepoint in 2019.

READ MORE: Kate recycles 10-year-old Alexander McQueen gown for Earthshot Prize

Underneath was a black turtleneck jumper that had some comparing his look to that of a Bond villain, or even the British spy himself. At the recent premier of No Time To Die, Daniel Craig wore a velvet jacket in fuschia.

William and Kate were simply following their own rules at the ceremony on Sunday night.

All guests had been told not to buy anything new for the event in keeping in line with the awards' aim to solve some of the world's most pressing climate issues - and reducing waste is one of the biggest.

Actress Emma Thompson said it was a "relief" she didn't have to buy anything new and chose an emerald green Stella McCartney suit she first wore to Buckingham Palace when she received her damehood for services to drama from Prince William in 2018.

READ MORE: Prince William sparks hopes of a reunion with Prince Harry following Earthshot Prize Awards

She also wore a $30 ring bought by her husband in New York City many years ago.

Harry Potter star Emma Watson wore a dress made from 10 different wedding gowns from Oxfam, in the ultimate example of upcycling.

Performances at the event were powered by 60 cyclists pedalling on bikes while the menu offered vegan and vegetarian meals only.