(CNN)Jimmy Micioni, a New Jersey man affectionately known as Uncle Jimmy to everyone who knew him, died in March at the age of 97.
However, little did anyone else know that stashed in his attic was a meticulously collected and cataloged sports card collection valued at more than $1 million.
While Micioni's nieces and nephews have gotten glimpses of his collection over the years through birthday gifts and visits to his home, they did not see or truly understand the size of his treasure trove of sports cards until after his death. Micioni's family was tasked with cleaning out his home in Boonton, in northern New Jersey, and that's when they discovered his vast collection.
"It was almost like a museum," Jeanne Griffith, Micioni's niece, told CNN affiliate WGAL. "It was amazing to see. There was baseball cards and memorabilia and pennants all over the entire basement walls and everything."
Among the treasures are autographed cards from baseball legends such as Babe Ruth, Lou Gehrig and Jimmie Foxx. Micioni mailed the cards to players for them to autograph, and he even saved the envelopes, according to WGAL.
The collection is up for sale at Wheatland Auction Services, which is run by Chuck and Stacey Whisman. The collection of cards is so large that they were broken up into multiple lots and are being offered in three different collections.
Wheatland Auction Services did not immediately respond to a request for comment from CNN.
"The family would just bring large drop-offs of items to us here, overwhelmingly so, and we would one at a time, box by box, row by row, sort through," Stacey told WGAL. "It was a treasure hunt. It was an exciting treasure hunt."
The cards were evaluated by Professional Sports Authenticator (PSA), a third-party grading and authentication company, according to its website.
"We've witnessed and graded many impressive collections and finds over our 30 years in the industry, but the Uncle Jimmy Collection ranks near the top in terms of volume, player selection and preservation," PSA President Steve Sloan told CNN.
"It's truly a remarkable assortment of cards that one man put together over nearly nine decades of collecting."
Sloan said he was impressed with the overall preservation of the cards, as some of the cards date back to the 1930s. He adds that the cards are "valued at north of $1 million, but could ultimately sell for several million."
The most valuable items are six different 1933 Goudey cards that were signed by Babe Ruth, and one of those cards just sold for $153,400 on Sunday. Sloan said "that's not even the best one of the bunch," and he believes the 1933 Goudey #149 card will sell for even more when it goes up for sale.