The Prince of Wales will call on world leaders and the business community to "think big" and "with urgency" to address the potentially catastrophic damage being done to the world's oceans.

Prince William's call to action comes as he teamed up with Sir David Attenborough in a social media video to talk about the harmful effects of over-fishing, pollution and temperature rise on our marine environment.

On Sunday, the royal will travel to the south of France to deliver what's been described as a "landmark speech" at the Blue Economy and Finance Forum in Monaco.

He is expected to say: "Halfway through this decisive decade, I call on all of you to think big in your actions.

"Let us act together with urgency and optimism while we still have the chance."

The forum, organised by the government of Monaco, the Prince Albert II of Monaco Foundation, and the Oceanographic Institute of Monaco, with support from France and Costa Rica, will bring together business leaders and government representatives committed to restoring the health of the oceans.

The ocean covers 70% of the Earth's surface and is essential to all life on Earth.

It generates half of the world's oxygen, regulates our climate and provides food for over three billion people worldwide.

The event takes place ahead of the 2025 UN Ocean Conference, which will be held in Nice next week.

William will speak alongside President Chaves Robles of Costa Rica, President Emmanuel Macron of France and Prince Albert II of Monaco.

At a time when Prince William is increasingly being portrayed as a global statesman, we're told these will be deliberately strong words from him.

A Kensington Palace spokesman added: "There should be no doubt that this speech is the Prince of Wales calling for action to save our oceans now.

"The world is watching. This is him using his platform to call for more to be done sooner rather than later."

To coincide with the event, and to attract a greater audience, a YouTube video has been posted by Kensington Palace, showing William and Sir David Attenborough laughing together as Sir David tries on his first-ever diving helmet.

But their conversation soon turns to more serious matters when they discuss Sir David's new film, Oceans, and the horrific examples of damage uncovered.

When William asks: "David, from what you've obviously seen over the years, what state would you say the oceans are in right now?"

Sir David replies: "The awful thing is that it's hidden from you and from me and most people.

"The thing which I am appalled by when I first saw the shots were taken for this film are what we have done to the deep ocean floor is just unspeakably awful.

"I mean, if you did anything remotely like it on land, everybody would be up in arms.

"If this film does anything, if it just shifts public awareness, it'll be very, very important, and I can only hope that people who see it will recognise that something must be done before we destroy this great treasure."

A hopeful message

But trying to end on a hopeful message, which is an important part of Prince William's approach to environmental issues, William asks: "Have you seen any stories where you feel that there is hope that we can turn this around?"

Sir David says: "What is heartening, really, is that we have the entree to people's front rooms.

"Whole families sitting at home in comfort can actually suddenly see this coming up. Films like this can expose something new and interesting."

Finalists from Prince William's Earthshot Prize are also due to attend the forum in Monaco. The 2025 Earthshot Awards will be held in Brazil later this year.