Lesotho Promise - Lesotho Promise. A 603-carat diamond, named the Lesotho Promise after the country in which it was found, was sold last week in Antwerp for $12.36 million. The giant raw diamond will most likely be cut into several smaller diamonds, which will have a collective value of approximately $20 million. The white diamond - the most popular color for a diamond to be - was the 15th largest ever found in the world, and the largest to be discovered this century.