Many people on social media thought it was the "Isadora" diamond Kate Hudson wore in "How to Lose a Guy in 10 Days." 

Not quite.

5 moments you missed from the 2019 Oscars

Lady Gaga borrowing the Isadora Diamond

— Taylor Mae (@taymae722)February 25, 2019

The massive yellow diamond that Lady Gaga wore around her neck at the 2019 Academy Awards Sunday night is, however, one of the largest yellow diamonds in the world, according to Tiffany & Co. The diamond was discovered in South Africa in 1877 and purchased by the jewelry store founder Charles Lewis Tiffany for $18,000. It was cut into a 128-carat diamond and displayed at many of Tiffany's exhibits around the world, including once in the window of the flagship store in New York City. The diamond lives in the flagship store on Fifth Avenue, on display and heavily guarded.

The diamond has only been worn three times in history: once by Mary Whitehouse at the Tiffany Ball in 1957 and again by Audrey Hepburn in 1961 for publicity photographs for "Breakfast at Tiffany's." Lady Gaga was the third person to wear the diamond at Sunday night's Oscars ceremony, where she took home the award for Best Original Song for "Shallow" from "A Star is Born." 

Bradley Cooper and Lady Gaga perform ‘Shallow’ from ‘A Star is Born’ at 2019 Oscars