After decades of collectors’ fairs, auctions and reissues by manufacturers, the world of baseball card collecting still has surprises up its sleeve.

Boonton, N.J., resident James Micioni, who passed away in March at the age of 97, left behind a collection of vintage baseball memorabilia to his family that is expected to net up to several million dollars at auction, per a report by NJ.com. The collection includes many baseball cards signed by some of the biggest stars the sport has ever known.

Headlining Micioni’s collection are six 1933 Babe Ruth cards, hand-signed by the Great Bambino, that could sell for more than $100,000. Micioni also owned cards signed by Jimmie Foxx and Lou Gehrig from the same 1933 Goudey set, along with a mint condition Reggie Jackson 1969 Topps rookie card, a near-mint Jackie Robinson card from Bowman’s 1949 collection and a mint 1965 Topps Pete Rose card.

Experts deemed the collection of Micioni, known to Boonton residents as “Uncle Jimmy,” to be one of the most incredible assortments of memorabilia ever assembled. All the pieces are authenticated, and the collection will be auctioned off as 2,000 separate lots, with the first 650 lots planned for an online auction beginning Sunday.

“Maybe once a decade something like this comes around,” said Chuck Whisman, owner of the auction’s host, Wheatland Auction Services. “The cool thing is, nobody knew of his collection. He just collected his whole life. He didn’t show it off to anyone.”

The first of the six Ruth cards will be part of the June 14 auction, with the rest slated for future auctions to be held over the next several months. Micioni’s collection also includes artifacts like a rare Mickey Mantle plastic plaque from 1963, original photos of Ruth and Gehrig taken by famous baseball photographer George Burke and ticket stubs from games played by Ruth, Robinson and Willie Mays.

“Overall, the preservation is terrific,” said Joe Orlando, president and CEO of Collectors Universe, the parent company of PSA, which authenticated the collection. “Because Uncle Jimmy preserved them so well, the colors retain their freshness and their brightness, so the eye appeal of the cards is tremendous because he took the time to preserve them the right way."

Micioni’s family told NJ.com that he never stood in line or paid for autographs, choosing to send handwritten letters to teams and players instead and including a return envelope. He lived in the same house for his entire life, never drove a car and was a staple in Boonton (population: 8,000). His relatives were aware he kept a baseball memorabilia collection, but they were unaware of its depth and value until his passing.