The Royal Mint has produced its first ever £50 coin which also has a face value for the same amount.
The fine silver coin has been launched to celebrate the year that the Queen became the nation's longest-reigning monarch.
The Royal Mint, whose history of producing British coinage goes back more than 1,000 years, said that this is the first time it has issued a £50 coin which also has a face value of £50.
Unusually for a coin from the Mint, the portraits on both sides of the coin are by the same artist - 33-year old Royal Mint engraver Jody Clark.
Clark designed the fifth definitive portrait of the Queen to appear on circulating coins since her accession to the throne in 1952. The portrait of the Queen started to appear on coins from March. It has been paired with his contemporary image of Britannia to appear on the new £50 commemorative coin.
The coin is being made available to buy on the Mint's website and 100,000 of the coins will be minted.
The first coin in the Royal Mint's "face value" range - a £20 for £20 coin marking the birth of Prince George - sold out within days. Also in the range, a £100 coin featuring Big Ben also sold out within days.
The Queen is now considered to be the longest reigning monarch in British history, having surpassed her great-grandmother Queen Victoria's record. The milestone was reached in September.
Clark said: "Having my portrait of the Queen selected for Britain's coinage was an incredible experience, but now, seeing the portrait combined with my Britannia design on the UK's new £50 coin is a double honour."