Prince William sat down with Sir David Attenborough for a candid chat as the legendary broadcaster and biologist releases a new documentary.

The Prince of Wales shared a clip on X (formerly Twitter) ahead of World Ocean Day tomorrow, saying that it was "fascinating to reflect on the wonder of the ocean and the legacy of a man who has dedicated his life to telling its story". In the clip, Prince William said to Sir David: "When you first went diving, we knew so little about the underwater world. Is that not fascinating for you to be one of the first people to be able to talk about that and see it?"

The broadcaster, biologist, and author replied: "Oh yes. Once Cousteau invented the Aqua-Lung and the face mask, that was the moment when, suddenly, you moved into a new world.

"You were flying alongside fish, which was an extraordinary experience. And the fish, of course, take no reaction to you, really, because they've never seen anything like you before. The underwater camerapersons are fantastic. They are people who are, I think, happier underwater than they are on land."

At one point, Sir David tried on an old diving helmet and Prince William laughed, saying: "Don't! You won't be able to get it off David!"

The full conversation, about a lifetime of exploration, the urgent challenges facing our seas, and the hope that lies in restoring and protecting them for generations to come, is on YouTube.

World Ocean Day promotes collective action for a healthy ocean and a stable climate. It has been recognised by the UN since 2008 and includes over 2,000 organisations in 180 countries.

This year, the day is focused on developing more opportunities for ocean and climate action, hoping to grow the movement for a more sustainable society and a healthy blue planet.