Lady Gaga was wearing one of the biggest diamonds in the world when she won her Oscar for best original song.
The rock, known as the Tiffany Diamond, was last worn by Audrey Hepburn in 1961.
It is reported to be worth between $30m and $50m (£23m-£38m).
Gaga showed it off to good effect by pairing it with a black strapless dress for the ceremony, and later changing into another black number with a plunging neckline.
“I’m wearing Alexander McQueen and Tiffany’s,” she told reporters on the red carpet.
Tiffany said the diamond was “released from the vault specifically for Lady Gaga” and that it “marks the first time in history that the legendary Tiffany Diamond has graced an awards show red carpet”.
The Tiffany Diamond was extracted from the Kimberley mines of South Africa in 1877, the company says, and was the largest yellow diamond found until then.
Initially measuring 287.42 carats, it was sent to Paris by Charles Lewis Tiffany, where it was cut to 128.54 carats and fashioned into a cushion shape.
It is “deemed one of the world’s largest and finest fancy yellow diamonds”, Tiffany says.
It made its appearance in Tiffany’s Fifth Avenue windows in 1955, and “could easily be seen from across the street”.
Six years later, Audrey Hepburn wore it in publicity photos for the movie Breakfast at Tiffany’s, in which she played eccentric cafe society girl Holly Golightly.
In 2012, on the 175th anniversary of Tiffany’s founding, it was reset in a “magnificent necklace of dazzling white diamonds”, the company says.
Gaga won her Oscar for the song Shallow from A Star is Born, and performed it with co-star Bradley Cooper at the ceremony.