Karl Kissner, 51, of Defiance, and his cousin, Karla Hench, said the stash of 700 cards belonged to their grandfather, Carl Hench, who died in the 1940s. Kissner discovered the items while cleaning out the attic of the family home where Carl Hench once lived, the Toledo (Ohio) Blade reported Friday.
The family soon discovered the value of the vintage baseball cards, which experts said include many cards in pristine condition, and decided to sell them at auction.
The first round of cards sold for a total $566,132 in a live and online auction operated by Heritage Auctions at the National Sports Collectors Convention in Baltimore.
Karla Hench said the cards brought "fantastic prices and we're very excited that we can all share in this find. It's like a gift from our grandfather to keep passing on."