Recently, Prince William attended the Earthshot Prize Awards in Cape Town, where he inspired the audience with his speech on protecting the planet. But people also noticed something interesting about his outfit. This choice wasn’t random, it has a clear message.

Prince William hopes that the Earthshot Prize will “change the world for good” over the next ten years, as he celebrated this year’s winners in Cape Town. Closing the ceremony, he called for people everywhere to join this “movement for change.”

The event, with 2,000 guests, focused on sustainability. Instead of a red carpet, guests walked a “green carpet” and were encouraged to wear eco-friendly outfits — either made from recycled materials or worn before. William joined in by wearing a vintage Prince of Wales check jacket and fully biodegradable, plastic-free shoes.