A T206 Honus Wagner tobacco card from 1909 sold for $6.6m on Monday, shattering the record for highest-selling sports card of all time.
The previous record of $5.2m belonged to a 1952 Topps Mickey Mantle card and the 2003-04 Upper Deck Exquisite Collection autographed rookie jersey card of LeBron James.
The T206 Wagner card is considered the holy grail of cards, given how few are known to exist.
"This Wagner stands out because of its condition," said Brian Dwyer, president of Robert Edward Auctions, which brokered the deal.
"There's only about 60 of these that we can confirm through various population reports and available grading data. Of those 60, most are rated poor, authentic or good, at best.
"This card is one of the best examples out there, and it's certainly one of the best examples available."
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Both parties wished to remain anonymous, though the seller was identified as an East Coast collector.
Wagner was part of the Baseball Hall of Fame's inaugural class in 1936 (along with Babe Ruth, Ty Cobb, Christy Mathewson, and Walter Johnson), playing from 1897 to 1917.
At the time baseball cards were being produced en masse and inserted into cigarette packs by companies like the American Tobacco Company, which is the company that produced the T206 Wagner card.