La Peregrina pearl 
The 55.95-carat pearl was originally acquired by King Phillip II of Spain in 1582, and was subsequently passed down through the Spanish monarchy until 1808, when it was obtained by Napoleon‘s brother Joseph Bonaparte. It was then held by Prince Louis Napoleon of France and the Duke and Duchess of Abercorn, until Richard Burton bought it in 1969 from Sotheby’s for $37,000.  He gave it to Elizabeth Taylor on Valentine’s Day as a gift.
Taylor commissioned Cartier to incorporate the La Peregrina pearl into a stunning diamond and ruby necklace which sold at Christie’s for $11.8 million.   Note the difference in the pearl weight in the above description and in the catalogue details. 
Details from Christie’s Catalogue:
Suspending a detachable drop-shaped natural pearl pendant, weighing approximately 202.24 grains or 50.56 carats, measuring approximately 17.35 – 17.90 x 25.50 mm, with an old mine-cut and rose-cut diamond and silver foliate bail, suspended from a circular-cut diamond flame motif set with a pear-shaped ruby, spaced by a detachable pear-shaped ruby and natural pearl link, to the two-strand necklace, comprising fifty-six natural pearls and four cultured pearls, intersected by eight circular-cut diamond and cushion-cut ruby flame motif plaques, mounted in platinum and gold, La Peregrina late 16th century; diamond bail early 19th century; natural pearl, diamond, ruby and cultured pearl necklace by Cartier 1972, 13½ ins., pendant may also be worn as a brooch, accompanied by the seed pearl and platinum neckchain from the time of the purchase at auction in 1969, 30¾ ins.

La Peregrina pearl 

The 55.95-carat pearl was originally acquired by King Phillip II of Spain in 1582, and was subsequently passed down through the Spanish monarchy until 1808, when it was obtained by Napoleon‘s brother Joseph Bonaparte. It was then held by Prince Louis Napoleon of France and the Duke and Duchess of Abercorn, until Richard Burton bought it in 1969 from Sotheby’s for $37,000.  He gave it to Elizabeth Taylor on Valentine’s Day as a gift.

Taylor commissioned Cartier to incorporate the La Peregrina pearl into a stunning diamond and ruby necklace which sold at Christie’s for $11.8 million.   Note the difference in the pearl weight in the above description and in the catalogue details. 

Details from Christie’s Catalogue:

Suspending a detachable drop-shaped natural pearl pendant, weighing approximately 202.24 grains or 50.56 carats, measuring approximately 17.35 – 17.90 x 25.50 mm, with an old mine-cut and rose-cut diamond and silver foliate bail, suspended from a circular-cut diamond flame motif set with a pear-shaped ruby, spaced by a detachable pear-shaped ruby and natural pearl link, to the two-strand necklace, comprising fifty-six natural pearls and four cultured pearls, intersected by eight circular-cut diamond and cushion-cut ruby flame motif plaques, mounted in platinum and gold, La Peregrina late 16th century; diamond bail early 19th century; natural pearl, diamond, ruby and cultured pearl necklace by Cartier 1972, 13½ ins., pendant may also be worn as a brooch, accompanied by the seed pearl and platinum neckchain from the time of the purchase at auction in 1969, 30¾ ins.