King Charles III coins released by the Royal Mint

The coins are part of a memorial collection for Her Majesty Queen Elizabeth II.

Each of the new commemorative coins bears the first coinage portrait of the King, designed by British sculptor Martin Jennings and personally approved by King Charles III.

"I was delighted to hear that the King likes the image," Mr Jennings told the Royal Mint.

"He was very interested in it and responded very positively to it."

To prepare for the process of designing His Majesty's official coinage portrait, Mr Jennings began his research by studying as many photographs of The King as he could.

"You collect as many photographic images of your subject as you can," he said.

"To present just one side of somebody's head, you have to understand how the head works in the round, so you examine all of these old photographs then settle on just one or two that give you the optimal impression of the side of the head that you are modelling.

"The piece is modelled in plaster larger than the size of the coin, so about the size of a dinner plate.

"I work by hand using tiny, tiny millimetres of material to model it. And eventually, once it is complete and cast in plaster, my original design can be digitally reduced so that the impression is the right size for a coin."

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In keeping with a tradition dating back centuries to the reign of Charles II, each monarch faces the alternate direction to their predecessor.

The portrait of King Charles III faces left, whereas Queen Elizabeth II faced right.

Avid Australian coin collector Joel Kandiah said there is massive hype surrounding this coin.

"It is likely that mintage will be unlimited for these coins, as the mint has indicated that there would be enough for everybody," he said on his Instagram page The History of Money.

He also explained the lettering - D.G.REX.F.D. - that surround the monarch's portrait on the coins.

D.G.REX stands for 'Dei Gratia Rex'. It's Latin for 'By the Grace of God, King'. For a female monarch it would be Dei Gratia Regina which translates to 'By the Grace of God, Queen'.

F.D. stands for 'Fidei Defensor'. This is also Latin and translates for 'Defender of the Faith'.

"These are Latin inscriptions of the full title of the King. They used to appear on Australia's pre-decimal coinage as well, up to 1964," Mr Kandiah explains.

The Royal Mint is yet to release a price for the coins, but he estimates, based on previous releases, it could be £12.50 to £15 ($21.63-$25.96 AUD) for each one, plus around $17 for postage.

With demand for the coins expected to be high, Mr Kandiah urged people to create an account with The Royal Mint now, and then log back on later when sales open.

They are available through www.royalmint.com from 9am BST. In Australia that's 4pm (Western Australia), 5.30pm (Northern Territory), 6pm (Queensland), 6.30pm (South Australia) and 7pm (NSW, ACT, Victoria and Tasmania).