The Golden Jubilee

Weight-545.67carats

Source-Premium Mine Africa

Current Owner-king Bhumibol Adulyadej(Thailand)

The "Unnamed Brown", as the Golden Jubilee was first known, was considered something of an ugly duckling by most. It was given to Gabriel Tolkowsky by De Beers for the purpose of testing special tools and cutting methods which had been developed for intended use on the flawless D-colour ("colourless") Centenary. These tools and methods had never been tested before, and the "Unnamed Brown" seemed the perfect guinea pig; it would be of no great loss should something go amiss.
Cutting and polishing the diamond was challenging because of its large surfaces, deep cracks from inside, and several inclusions. The diamond was cut in a specially designed underground room that was free from vibrations. It took two years to bring it to its current state.[1]
To the surprise of all concerned, what resulted was a yellow-brown diamond in a fire rose cushion cut, outweighing Cullinan I by 15.37 carats (3.07 g). The stone remained largely unknown to the outside world, as the Golden Jubilee's sister, the Centenary, had already been selected and promoted to herald De Beer's centennial celebrations in 1988.
The unnamed diamond had earlier been brought to Thailand by the Thai Diamond Manufacturers Association to be exhibited in the Thai Board of Investment Exhibition in Laem Chabang. There was a mile-long queue to see the diamond, which outshone all other exhibits.

The diamond is valued at 4-12 million US dollars