A postage stamp described as "the Mona Lisa" and "the Mount Everest" of stamp collecting for the past 100 years could fetch as much as $20 million in an auction tonight at Sotheby's Auction House in New York.

The British Guiana One-Cent Magenta stamp was first printed in 1856 and is the sole surviving One-Cent of the entire 1856 issue produced in Georgetown, British Guiana, according to Sotheby's.

The stamp was lost and then rediscovered by a 12-year-old Scottish boy living in South America in 1873.

"It's passed through the greatest stamp collections of the world," said Sotheby's David Redden, who appeared on " Good Morning America" with the stamp and the security guard who travels everywhere the stamp goes.

"It was bid on by George the 5 th of England," Redden said.

The stamp was most recently in the collection of John E. du Pont, an heir to the du Pont fortune who died in 2010 while in jail for murder. Du Pont, like all previous owners of the stamp, etched his initials in the back of the stamp.

"It is the Mona Lisa of stamps," said Redden. "It's been the most famous stamp in the world for the last 100 years."

Redden says the stamp was used at one time but since then has been "looked over very carefully."

If the roughly one square inch of paper sells for its expected $10 million to $20 million, the stamp, by size, will be the most valuable man-made item in the world.