The first stamp was created in Great Britain ... There are at least 86 known in existence (only 100 were ever printed), but the one sold in 2018 is the most expensive because it was locked away ...

And earlier this week, Number 49, which resurfaced in 2018 after spending decades tucked away in a safe-deposit box, fetched $2 million at auction, making it the most expensive U.S. stamp ever sold.