A rare Edward VIII gold sovereign has gone on display showing how the monarch broke with tradition - by demanding his profile faced in the wrong direction.

Edward thought his left side, showing the side parting in his hair, was better than his right, which featured a solid fringe, and insisted this was used.

He was breaking with tradition because coins struck following the accession of a monarch normally show the new King or Queen looking in the opposite direction to royal profiles on their predecessor's coins.

The gold sovereign - part of a commemorative set - was never issued because just as the Royal Mint was gearing up to produce a full set of coins the King dramatically abdicated, renouncing the throne on December 10 1936 to be with American divorcee Wallis Simpson.

At the time the Royal Mint's reducing machines were at work miniaturising the designs to coin and medal sizes and punches and dies for striking the coins were being made.

Coin production was scheduled to begin at 8am on January 1 1937 but was abandoned, and today all that exists are some extremely rare patterns and trial pieces including the sovereign, and a number of coins with private collectors.

Humphrey Paget created the coinage portrait of Edward and on one occasion when he went to have a sitting with the King, the monarch did not turn up and could not be found and a courtier reportedly said "this would never have happened in his father's time".

Graham Dyer, senior curator at the Royal Mint, said: "The tradition of the monarch's head facing in the opposite direction to his predecessor dates back to King Charles II in the 17th Century, so according to this tradition, Edward VIII's effigy should have faced to the right.

"Instead, Edward VIII insisted that his profile face left on the coin, so that the parting of his hair was visible. He thought that this was his better side, and that inclusion of the parting would break up what might otherwise look like a solid fringe of hair."

Following his abdication, Edward VIII requested a set of the coins as a memento, but his brother George VI declined as they had never been issued, were not deemed to be official UK coinage and had not gone through the Royal Proclamation process.

Edward, who was known to his family by his 7th forename of David, and Mrs Simpson married in June 1937 following her second divorce.

They became the Duke and Duchess of Windsor and spent most of the rest of their lives in exile in France, with the duke dying in 1972 and the duchess in 1986.

The rare sovereign has gone on display at the Royal Mint Experience, the Royal Mint's new visitor attraction in Llantrisant, South Wales.