As a 10-year-old in the 1950s Thomas Newman did what other boys his age did: he collected baseball cards.

Over a couple of years Newman assembled a treasured collection that was not equally prized by his mother, who thought of the cards as garbage and tossed them out. The loss inspired a decades-long passion to recoup what he'd lost. And then some.

"My dad began collecting in the early 1980s starting with baseball cards from 1957 and 1959 when he was ten to twelve years old," his son Stewart Newman said. "Those were replacements for the treasured cards of his youth that he kept in shoeboxes as a youngster and that his mom later threw out."

Eventually Newman, who died from COVID-19 in January, traveled the country piecing together an extensive stockpile of baseball and other sports memorabilia that auctioneers estimate is now worth about $20 million. And next month, they'll be up for auction via Memory Lane Auctions from June 21 through July 10.

The sale will include an mint-condition 1933 Babe Ruth card that could become the most expensive of all time. Memory Lane Auctions President JP Cohen described the "Sultan of Swat" card, one of four in the world, as "the finest known of its kind."