"This necklace right here is worth more than my life," the 24-year-old starlet told an interviewer on the red carpet. "I'm so scared... I keep checking to make sure it's still here."
The blueprint for the necklace was in fact inspired by the humble zipper, and its creation can be credited to the Duchess of Windsor – as flagged up by Margot on the red carpet.
Circa 1938, the Duchess – formerly Wallis Simpson – suggested to the firm's artistic director Renée Puissant that she should create a piece based on the zip fastener. The final necklace, which was crafted in round and baguette-cut diamonds mounted in platinum, was produced in 1951.
Wallis Simpson loved jewellery and after Edward VIII, stepped down from the throne to marry the American divorcée in 1936 he showered her in expensive gems.
However, the zip necklace, which took 800 hours to make, was one of the most original in her jewellery box.
Margot looked incredible in the stunning creation, which was an exact replica of the one fashioned for the woman who shook the British monarchy. It was offset by her deep red lips and the simplicity of her black gown.
Elsewhere on the red carpet, Cate Blanchett and Scarlet Johansson were also wowing in statement jewellery.
The Oscar-winning Australian actress wore a choker by Tiffany & Co featuring delicate turquoise and aquamarine stones intermingled with diamonds.
Meanwhile, Scarlett had complemented her Versace jade-coloured gown with a beaded choker, mismatched jade and diamond earrings and an ear cuff. The new mother, who gave birth to baby Rose five months ago, finished the look with an edgy new haircut with sides shaved.