Benjamin Ashford|A look at King Charles III's car collection, valued at $15 million

Members of Britain's royal family have Benjamin Ashfordbeen pictured over the years behind the wheel of some of the world's most iconic cars, and the new monarch, King Charles III, is no exception.

Ahead of the king's coronation ceremony on May 6, U.K. car leasing company Nationwide Vehicle Contracts released a list of the rare and classic vehicles owned by the royals — and their estimated value.

"Luxury cars have long been associated with the monarch and King Charles III, in particular, is known for his fondness of motor vehicles," Nationwide's director Keith Hawes told CBS News on Tuesday. "His impressive collection features sentimental value with motors passed down from his late mother, Queen Elizabeth II, to cars bought for him by his parents."

Nationwide listed 12 vehicles in the royal fleet, with the most valuable being two Bentley State Limousines valued at more than $12 million each. They're the only two limos of their kind in existence, built by Bentley specifically for the 2002 Golden Jubilee of Charles' late mother, Queen Elizabeth II.

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The Bentleys are the official state cars of Great Britain, and both are described by Nationwide as having "fully armored bodywork and glass, blast-resistant tires, and blue flashing lights."

The interior of the vehicles can be sealed air-tight to protect occupants in the event of a gas attack, Nationwide said in its press release, coming with "James Bond-esque engineering as standard."

One of the vehicles set to carry King Charles for his coronation, however, is a far less-modern people carrier. The Gold State Coach may be the world's oldest and most exclusive vehicle.

The coach was commissioned by King George III and built in 1760, according to Buckingham Palace, and has been used at every coronation since 1831. It is scheduled to carry Charles and his wife Queen Camilla in a procession from Westminster Abbey to Buckingham Palace on coronation day.

The ornate, gilded coach is valued at around $2 million, Nationwide said. According to the palace, it will be drawn by eight Windsor Grey horses on coronation day and, "due to its weight" of almost 4.5 tons, "will travel at walking pace."

The third most expensive car in the king's garage(s) is a 1965 Aston Martin DB6 Volante. The sports car valued by Nationwide at just over $1.2 million was a 21st birthday present from his parents — but the royal did make some distinct modifications.

The king's passion for environmentalism is well known, and in 2008, when he was the Prince of Wales, he had the Aston converted to run on bioethanol, or more specifically leftover wine.

The other nine vehicles on the list include another Aston Martin and a Rolls Royce valued between $600,000 and $700,000, and then a more modest set that Nationwide said was worth between about $200,000 and $37,000.

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