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Margot’s exact is currently not for sale. It may be vintage or custom. Most likely custom, considering it parallels the modern necklace, but is slightly altered to fit the entire outfit made for this look.

Her pearls are the same size, whereas the selling product is a Pearlescent and Crystal Degrade Short Necklace

One with matching sized pearls but different crystal design is selling: GIVENCHY x SWAROVSKI CRYSTAL faux PEARL necklace