While cleaning out their late mother's California loft last Christmas, three brothers made a life-changing discovery under a pile of faded newspapers: one of the first Superman comics ever made.

An original copy of the June 1939 first edition of the Man of Steel's adventures was in remarkably pristine condition.

Now it has become the highest-priced comic book ever sold, fetching $9.12m (£7m) at auction.

Texas-based Heritage Auctions, which hosted Thursday's sale, called it the "pinnacle of comic collecting".

The brothers found six comic books, including Superman #1, in the loft underneath a stack of newspapers inside a cardboard box and surrounded by cobwebs in 2024, Heritage said.

They waited a few months before contacting the auction house, but once they did, Heritage Auctions vice-president Lon Allen visited them in San Francisco within days, according to the auction house.

The brothers, who have chosen to withhold their names, are "in their 50s and 60s, and their mom had always told them she had an expensive comics collection but never showed them", Mr Allen said.

"It's a twist on the old 'Mom threw away my comics' story."

Their mother had held onto the comic books since she and her brother bought them between the Great Depression and the beginning of World War Two, Heritage said.

Mr Allen added that the cool northern California climate was perfect for preserving old paper.

"If it had been in an attic here in Texas, it would have been ruined," he said.

That helped CGC, a large third-party comics grading service, give this copy of Superman #1 a 9.0 rating on a 10-point scale, topping the previous record of 8.5.

And at its sale price of over $9m, including buyer's premium, Superman #1 easily beat the previous highest-priced comic book ever sold by $3m.

Action Comics No. 1, the 1938 work that first introduced Superman, sold for $6m last year.

The youngest brother said in a press release by the auction house that the box had remained forgotten in the back of attic.

"As the years unfolded, life brought about a series of losses and changes," he said. "The demands of everyday survival took centre stage, and the box of comics, once set aside with care and intention, was forgotten. Until last Christmas."

He added: "This isn't simply a story about old paper and ink. This was never just about a collectible.

"This is a testament to memory, family and the unexpected ways the past finds its way back to us."