The royal, who was made Duke of Edinburgh last year, encountered him in the grounds of Plantation House, the governor's official residence on St Helena, a British overseas territory in the South Atlantic Ocean.

The reptile has lived for so long that Edward's grandparents King George VI and Queen Elizabeth (later the Queen Mother), met him in 1947 when he was 115 years old.

The duke's late mother, Queen Elizabeth II, also met Jonathan when she was Princess Elizabeth on the same trip.

In 1957, Prince Philip, the late Duke of Edinburgh, fed Jonathan, then aged 125, during a visit to the island.

Jonathan, who is believed to have been born in 1832, has lived during eight British monarchs including the 63-year reign of Queen Victoria.

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He was brought to St Helena from the Seychelles in 1882 along with three other tortoises at around 50 years of age, and he celebrated his official 191st birthday last December.

At just 47 square miles, St Helena is a third of the size of the Isle of Wight, and its nearest landmass is Ascension Island, which is 807 miles to the northwest.

Edward is the first royal to visit since the Princess Royal travelled there 22 years ago in 2002.

The duke's trip was commemorated with a public holiday on the island. His four-day stay also includes opening an airport, meeting community leaders and learning about wildlife conservation efforts.

Governor Nigel Phillips described it as a "special occasion", with the holiday "allowing the entire community to join this opportunity to celebrate all that is great about the culture and environment of this remarkable island".

His tour comes as the King prepares to undergo hospital treatment for an enlarged prostate, and the Princess of Wales remains in hospital after abdominal surgery.