Mickey Mantle's last Yankees jersey just netted a small fortune at auction ... raking in a staggering $2.2 MILLION!!!
Officials at Heritage Auctions tell TMZ Sports ... the sale just closed over the weekend, and it was a historic one, because it's now the highest price ever paid for a Mick jersey.
In fact, the price tag was so high, it was hundreds of thousands of dollars more than what experts initially thought it could fetch.
As for why it sold for so much .