Givenchy died in his sleep Saturday night, according to his longtime partner, designer Philippe Venet.
Hepburn famously wore Givenchy's designs in several of her movies, including "Breakfast at Tiffany's" and "Sabrina" -- and she went on to become an ambassador for his brand.
He might not brag about this one, but Lindsay Lohan famously wore Givenchy back in 2012 ... during one of her many, many, many court appearances.
Givenchy founded his design house in 1952, and it's now owned by the luxury fashion company LVMH. He was 91.