Interesting story from 9 years ago: https://www.thedailybeast.com/the-137-carat-diamond-lost-for...

"The 137-Carat Diamond Lost Forever"

The Florentine Diamond enjoyed centuries of adventure, a slew of noble owners, and a position of prestige, before it went missing for what is likely the final time.

  Whether its adventure covertly continues today or whether it was lost forever, the Florentine diamond—in its massive, multi-faceted gleaming yellow form—is unlikely to ever be publicly seen again.

tl;dr: It never went missing, it was in their bank vault.

No story here.