A pure gold English penny, which dates back about 1,200 years, could fetch up to £150,000 at auction.
Experts say the coin is the earliest pure gold English penny
The coin was stumbled upon by a man
walking along the banks of the River Ivel in Bedfordshire.
It was struck in London and bears the image of King Coenwulf, who ruled
7th Century kingdom Mercia, in central England.
The artefact, which was found in 2001, will go under the hammer on Wednesday at London auction house Spink.
Speaking of his initial reaction, Richard Bishop, coin specialist at Spink, said: "It took a little while for this to sink in.
"Obviously, it was something special but I had no idea how important it was."
The precise site where the coin was discovered has been kept secret.
Proceeds from the sale will be split between the landowner and the finder, both of whom wish to remain anonymous.
Experts have valued the coin, which weighs 4.33 grams (a fraction of an ounce), at between £120,000 and £150,000 and say it is the earliest pure gold