King Charles was back at it yesterday as he surprised walkers enjoying a rare sunny day on the south coast of England by taking a walk on a "marvellous" new path named after him.

Shortly after bidding the Nigerian President a fond farewell at Windsor Castle following the two-day state visit, the monarch arrived at a reception hosted by the South Downs National Park Authority at the Salt Marsh Café.

After a few restorative sips of tea, the King began a country walk that stretched for 2km and took about an hour, including pauses for plaque unveiling.

As he walked by, several members of the public, unaware he was in the area, gaped and asked, "Is that actually the King?" "The King? Are you serious?" said one young man. Another, topless and barefoot on the stony path, simply nodded and allowed his Yorkshire terrier to sniff the monarch's feet.

Charles then joked with a group of cyclists that their e-bikes were "cheating!" and told walkers he hoped he had not interrupted their peace and quiet. He called the project "marvellous", and the work people were doing to finish it "fantastic".

His Majesty's visit marked the official inauguration of the King Charles III England Coast Path and the opening of the Seven Sisters National Nature Reserve.

It comes at the halfway point of a project to create 25 National Nature Reserves since his coronation in 2023. The coast path will eventually stretch 2,700 miles - the longest continuous managed coastal walking route in the world - and is named after him in honour of his love of conserving the natural world.

Tony Juniper, chairman of Natural England, told the King it was "wonderful you're here to see it", given it is one of the "things closest to your heart".

"And the path will always be there?" the King clarified. "It's the longest one anywhere?"

Told it was the "ultimate way of connecting with the coast", the King remarked on the opportunity for cold water swimming, saying: "They're all doing it!"

The King's daughter-in-law, the Princess of Wales, has previously revealed that even she is a fan of the sport: "the colder, the better", she has laughed.

After the walk, Mr Juniper revealed what he and the King had discussed. He said: "We don't do small talk with His Majesty, not when he's out looking at nature. He's so interested in animals, plants, geology...

"He finds it fascinating and uplifting to see the work being done here, working together to bring this landscape and vision to life."

The Seven Sisters National Nature Reserve is the 13th of the 25 planned National Nature Reserves by 2028.

The King Charles III England Coast Path is a 2,700-mile National Trail, designed to connect landmarks, unlock parts of England's coastline for public access for the first time, and encourage the public to spend more time in nature.