A family has discovered a stack of century-old baseball cards that can potentially be worth millions of dollars. Karl Kissner had been sifting through his grandfather's attic in Ohio, when he and his family came across a dusty cardboard box containing hundreds of baseball cards which had been under a wooden dollhouse all this time, according to AP.

Despite being over 100 years old, cards are said to be in perfect pristine condition, and the discovery is being hailed as one of the most exciting finds in sports card collecting. The cards apparently originate from a rare series issued around 1910.

Kissner told AP, "It's like finding the Mona Lisa in the attic." About 700 cards were found in the box.

Sports card experts and enthusiasts are impressed at the rare collection. "Every future find will ultimately be compared to this," said Joe Orlando, president of Professional Sports Authenticator.

37 of the cards, which are deemed the best, is expected to rake in half a million dollars at an upcoming auction which will be held during the National Sports Collectors Convention in Baltimore in August this year.

Overall, the cards can be worth up to $3 million, which include baseball legends Christy Mathewson, Connie Mack, Ty Cobb, Cy Young and Honus Wagner.

The cards belonged to Kissner's grandfather, Carl Hench, who passed away in the 1940s. Hench owned a meat market and the family believe that he got those cards as a promotional item from a candy company that handed them out with caramels.

"We guess he stuck them in the attic and forgot about them," Kissner said. "They remained there frozen in time."

Hench's daughters lived in the house after he and his wife passed away, before the house was passed on to their nieces and nephews. Kissner, 51, was put in charge of the estate after their aunt Jean Hench passed away last year.

After finding the green box with the cards inside in February, the family had put it aside. But soon Kissner decided to do a little probing and realized that they might be holding something very valuable. He soon put it in a bank vault before sending some of the cards to expert Peter Calderon at Heritage Auctions in Dallas. Calderon was shocked to see the cards in such pristine condition. "You just don't see them this nice," he said.

The cards are from the E98 series that consisted of 30 players. Half of them were Hall of Famers. Although auctioneers have come across these cards, many of them were ruffed up and worn out. However, these cards were graded 9 - which means almost perfect. A Honus Wagner card was a 10.