A rare and revolutionary watch which belonged to King George III is expected to fetch up to £1 million at auction.

The gold Tourbillon Watch represented cutting-edge technology in the early 19th century and was made by the French watchmaking “genius” Abraham-Louis Breguet.

Breguet was the celebrity watchmaker of his era and his creations were sought after by all the crowned heads of Europe, from Marie Antoinette and the King of Spain to Napoleon and Tsar Alexander I.

The watch, which will go under the hammer at Sotheby’s in London on July 14, features Breguet’s groundbreaking Tourbillon invention – a mechanism that increases the accuracy of a watch by fighting gravity and correcting for positional error.

It is considered one of Breguet’s most important timepieces and was the first Tourbillon he ever sold commercially.

It had to be discreetly bought by the King – who was passionate about the sciences and horology – in 1808 for what was the huge sum of FF 4,800 in the midst of the Napoleonic Wars, when it would have been unthinkable for the UK’s monarch to purchase a French watch.

To prevent the chance of its seizure, Breguet only signed the Tourbillon carriage inside the watch.

In the end, George III never actually fully paid for it and the Georgian Papers archive contains a bill reminder for an outstanding payment.

Daryn Schnipper, worldwide chair of Sotheby’s watch division, said: “Abraham-Louis Breguet watches were the theory of everything in the early 19th century, incorporating all the scientific discoveries of the past centuries, the philosophy of the Enlightenment and the great vision of a man who revolutionised watchmaking and placed time and precision at the core of modern society.

“When you hold the watch he made for George III, you instantly know you are in the presence of something truly exceptional.”

She added: “This watch not only captures Breguet’s genius – the ability to conceal layers of complexity behind apparent simplicity – it also encapsulates why historic timepieces are so relevant today.

“They transcend the function of mere timekeeping to tell us the history of the modern world.”

Engraved with George III’s royal cypher featuring a crown and the letters G & R, the watch is the only known four-minute Tourbillon with a dial in English and a thermometer.

It also features the indication “Whirling About Regulator”, translated from the French “Regulateur a Tourbillon”.