(CNN) -- The comic debut of Superman has sold for an out-of-this-world price.
The copy of Action Comics No. 1 from 1938, which features the first appearance of the "Man of Steel" was bought by an undisclosed buyer for a record $1.5 million Monday on the online auction site ComicConnect.com.
"This is the Holy Grail of Holy Grails," said Vincent Zurzolo, co-owner of the Web site.
A copy of the same issue sold for $1 million in February, but this one fetched a higher price because it is in better condition. It was stored inside a movie magazine for the past 50 years, Zurzolo said.
"The book looks like it just came off the presses yesterday," said Zurzolo. "The colors are extremely vivid, the whites behind the 'Action Comics' logo are snow white. It's just a stunning copy -- it almost looks brand new."
The sale of the Superman book marks the third time this year that a record was set for the sale of a comic book. The other copy of "Action Comics" No. 1 held onto its record for only three days before a comic book featuring Batman's debut sold for $75,000 more at an auction in Dallas, Texas.
It's widely believed that there are 50 to 100 copies of Action Comics No. 1 floating around, which makes it exceedingly rare. However, the copy sold Monday has received the highest rating to date from the Certified Guaranty Company, an independent comic grading company in Sarasota, Florida. The company inspects comic books for imperfections, ranging from yellowing to slight creases.
J.C. Vaughn, the associate publisher of The Overstreet Comic Book Price Guide, an annual publication considered the authority on comic book pricing, said the Action Comic No. 1 book sold Monday is worth every penny.
"The older any comic book gets, obviously the more unlikely you'll find it with a high rating," said Vaughn. "A book this old, featuring Superman's first appearance? I think this book warrants the price."
Back in 1938, there were 200,000 of these first editions printed and 130,000 sold, said Vaughn. The 70,000 other copies were destroyed.
Zurzolo said it could be a while before another comic book sets a new mark, because only a few other comics have this type of value.
"You will see a lot of very high-priced comic books selling in the next few years," he said. "But until these books hit the market again I don't think you'll see the same exact type of numbers in the near future."
ComicConnect wouldn't reveal the buyer of the $1.5 million Superman book.
"Our buyer, much like most of the superheroes out there, has a secret identity and would rather remain that way," Zurzolo said.
However, he added that the customer has a tremendous passion for superhero comic books and is especially fond of Superman.
"Superman was the first superhero," said Zurzolo. "Without Superman there would be no Batman, Spider Man, Wolverine, Wonder Woman -- they all came about because of the immense success of Action Comics and the first appearance of Superman."
Alex Rae, the back issue buyer for Midtown Comics, one of the nation's largest comic book dealers located in New York, said if he had his choice of any comic book in the world, it would be the one just purchased.
"It revolutionized the comic book industry," he said.
CNN Radio's Matt Cherry and CNN's Edmund DeMarche contributed to this report.