The Hope Diamond's still the biggest blue diamond on display at the Smithsonian, but now it's got some competition.
It's the first time in more than a half-century that the Wittelsbach gem has been on public display, and it will remain at the museum until Aug. 1.
Both diamonds first became known in the 17th century and while they are together scientists plan tests in hopes of learning if they came from the same mine in India where the Hope is known to have originated.
The Wittelsbach Diamond was first reported in the 1660s when Philip IV of Spain gave it to his daughter, Infanta Margarita Teresa, who was to marry Emperor Leopold I of Austria.
In 1722 it became the property of the Wittelsbachs, the ruling family of Bavaria. After World War I, Bavaria became a republic and the diamond was eventually sold at a Christie's auction in 1931.
In an incident that has never fully been explained, however, the Wittelsbach-Graff Diamond disappeared before the auction and was replaced by a worthless piece of blue, cut glass, according to Diamonds.net.
The actual Wittelsbach-Graff Diamond resurfaced in Belgium in 1951 and was eventually displayed — without attribution — at the World Exhibition in Brussels in 1958. The diamond was correctly identified in 1962 by Joseph Komkommer, a Belgian gem expert.
Christie's of London then auctioned it off in Dec. 2008 and sold to jeweler Laurence Graff, chairman of Graff Diamonds International Ltd. for $24.3 million.
"To have two of the world's most historical stones — the Wittelsbach-Graff and the Hope Diamond — displayed together, is a testament to the stones' history and importance," Graff said in a statement. "I believe the diamond's appearance at the Smithsonian will represent another significant chapter in its remarkable history."
Graff is lending the stone not only for exhibition but also research, according to the Washington Post.
The Hope Diamond was formed more than one billion years ago. It surfaced after a volcanic eruption and was discovered in the 17th century. It's believed that King George IV of England bought the re-cut in 1820; and after his death Henry Philip Hope purchased it, and the diamond still bears Hope's name today.
Smithsonian officials declined to estimate a value for the Hope Diamond, simply referring to it as priceless.