A single gold coin could fetch more than $1 million as ancient coin collection goes to auction after 100 years of secrecy

• A historic gold coin will kick off the sale of one of the most valuable privately owned collections.
• The 1496 King Hans Gold Noble coin is part of the prized L.E. Bruun collection, which is valued at $72 million.
• The collection has been kept in a secret location for years thanks to a stipulation in Bruun's will.

A rare Danish gold coin could fetch more than $1 million when it goes to auction next month, kicking off the sale of one of the most mysterious coin collections ever.

The 1496 King Hans Gold Noble coin is part of the collection that once belonged to Danish businessman and butter tycoon Lars Emil Bruun.

Brunn spent decades compiling the 20,000 or so coins, bank notes, medals, and tokens that make up the set. The collection has been kept out of the public eye for over a century due to a stipulation in Bruun's will that forbade the sale of the coins until at least a century after his death in 1923.

Following the devastation of World War I , Brunn decided his collection should be saved as backup reserves for Denmark should a second war hurt Europe. Since 2011, the coins have been kept in a secret location.

The collection is estimated to be worth about $72 million, making it the most valuable privately-owned coin collection to ever go to auction, according to Stack's Bowers , the coin dealer and auction house overseeing the sale.

The crown jewel of the collection is the gold noble, which has a pre-sale estimate of $327,000 to $655,000 but which could sell for more than $1 million at auction, according to the auction house.

Dating back to the late 15th century, the large coin is one of the oldest Scandinavian gold coins of all time, Stack's Bowers said in a Tuesday press release. Among the noble's key characteristics are its clearly visible and intricate details, an even flan, traces of the original luster, and no traces of mounting, according to the auction house.

"In short, it is an almost unbelievable survivor from the late Middle ages, and just as worthy in a collection of medieval art as in a coin collection," the sellers said in a statement.

Several Danish gold nobles were struck between 1496 and 1532 for Danish Kings Hans, Christian II, and Frederik I, according to Stack's Bowers. Only 20 coins of its type remain, and most of them are housed in the National Museum of Denmark — making this privately sold noble quite the catch, according to the auction house.

The specific reason for this noble's minting remains unknown, but Stack's Bowers said the coin was likely struck for the king's personal use as a gift for foreign dignitaries at a prominent courtly event in Denmark or abroad.

The coin was owned by the then director of the National Museum of Denmark, Christian Jurgensen Thomsen, in the mid 19th century. A count later bought the coin at auction in 1876 before the noble made its way to Bruun's collection.

Bruun's collection will be sold in a series of auctions over the course of several years starting next month.

The proceeds from the sales are set to go to the butter magnate's heirs.