(CNN) — A copy of the first ever issue of “ Superman ,” discovered in a Californian attic last year, has become the most expensive comic ever sold, fetching $9.12 million at auction .

Three brothers from northern California discovered the issue of “Superman #1” while clearing out their mother’s attic after her death. The 1939 comic had been kept in a cardboard box, protected by just a pile of old newspapers.

Nevertheless the comic, which originally sold for 10 cents, was found to be so well preserved that it was deemed the “highest ever graded copy” by Dallas-based auction house Heritage Auctions, which made the record-breaking sale on Thursday.

The brothers, who have not been named, found a collection of old comics while clearing out their mother’s property over the holiday season

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