Prince William has made a surprise appearance on the Graham Norton Show ­– sharing the famous red sofa with Australians Cate Blanchett and Robert Irwin.

The episode, recorded on Thursday evening (UK time), is due to air on the BBC on Friday night.

The Prince of Wales’ appearance – the first-ever by a British royal – had not been announced in advance and reportedly caught the audience off guard, with gasps heard alongside the cheers as he walked on stage.

It was part of a special edition of the show marking the Earthshot Prize, an initiative founded by Prince William in 2020 to encourage efforts to protect and restore the world’s natural environment.

Australian wildlife warrior Irwin is a global ambassador for the prize, while Blanchett is a member of the Earthshot Prize Council. Also part of the episode was Emmy-winning English actor Hannah Waddingham (Ted Lasso), who hosted the prize’s 2023 awards ceremony in Singapore.

Talkshow host Norton spoke to the three other guests about their careers and Earthshot – which will announce its 2026 winners in Mumbai next month – before William joined them on the sofa.

“They discussed the need to pair optimism and urgency when tackling climate change,” the BBC reported.

William also apparently helped judge who would survive the ‘big red chair’. Photo: PA

The prince is also said to have spoken about his long-time support for English soccer club Aston Villa and his love of both “deep-thinking” and action films, especially those by Oscar winning director Christopher Nolan.

“His films are fantastic – The Dark Knight series is psychologically dark and deep and I absolutely love that. He takes concepts that are completely out there and makes them incredibly entertaining,” he told Norton.

And William revealed his family is hooked on the current UK season of The Celebrity Traitors.

“I love it, the family love it. Charlotte and Louis are obsessed with it. It’s really good telly,” he said.

Robert Irwin and William rode an electric bus together in London in June. Photo: AAP

Irwin and William teamed up in London earlier this year for an Earthshot Prize event during which they rode together on an electric green bus.

At the time, the 22-year-old Aussie was effusive about William’s passion for the environment and his leadership of the Earthshot Prize, telling HELLO! magazine the prince “cares very, very deeply”.

“He’s been doing this for a very long time, and I really think that he’s seen first-hand what it is that the world needs, and I think it’s just fantastic that he uses his platform to unite people,” Irwin said.

Earthshot’s stated mission is to “find, celebrate and scale the solutions that will repair our planet by 2030”.

Each year it selects a shortlist of the “most impactful solutions” submitted to meet its five specific goals – restore nature, clean our air, revive our oceans, build a waste-free world and fix our climate – with five winners awarded £1 million ($A1.9 million).

Irwin will join a line-up of other celebrity guests for the November 17 winners announcement in Mumbai, including his fellow Earthshot ambassador, South African actor and TV personality Nomzamo Mbatha, film star Rami Malek and celebrated Indian cricketer Sachin Tendulkar.