The first new-look stamps featuring the portrait of King Charles have been unveiled by Royal Mail.

While the stamps won't go on sale until April - and only once all stocks featuring the Queen have been used up - this is the first time the postal services has released an image of how the new definitive stamps will look.

The King's image is an adapted version of the portrait created for the Royal Mint for new UK coins and shows the monarch facing to the left - without a crown.

A definitive stamp - also sometimes called an every day stamp - consists solely of a monarch's head against a plain coloured background alongside the value of the stamp itself.

The use of the coin image is a continuation of a long tradition, says Royal Mail, stretching back to the creation of the Penny Black in 1840 featuring the portrait of Queen Victoria.

But in a sign of the times, the King’s effigy also now appears alongside the new style high-tech barcode, which was first added to stamps last year, printed in a matching colour and will enable Royal Mail to add extra security features to post as the technology develops.

Plum purple is the colour given to 1st Class stamps, Holly Green for 2nd, Marine Turquoise for 1st Class Large and Dark Pine Green is the colour for 2nd Class Large.

The King's stamps will go on general sale from April 4 but customers and collectors wishing to get their hands on some of the first to be released can already register their interest here.

Shops and post offices however will continue to sell all their existing stocks of definitive stamps featuring Her Late Majesty The Queen to minimise the environmental impact of the change in monarch - in line with the King's wishes - and will only be supplied with the new stamps when existing stocks at Royal Mail have been exhausted

King Charles becomes the seventh monarch to appear on a Definitive stamp. The first being Queen Victoria who appeared on the Penny Black in 1840, followed by Edward VII, George V, Edward VIII, George VI, Queen Elizabeth II and now King Charles III.

Simon Thompson, CEO of Royal Mail said: “Ever since the Penny Black was issued in the reign of Queen Victoria, British stamps have carried the image of the reigning monarch. The Definitive stamp has become a recognisable symbol of each reign.

"Uniquely, British stamps do not have the country of origin printed on them as the image of the monarch is sufficient. So today is a hugely important milestone for Royal Mail and the country as we reveal the image of the new King Charles Definitive.”

The new 1st Class King Charles stamp will also form part of a special exhibition of Great Britain’s definitive stamps at the Postal Museum in London. Called ‘The King’s Stamp’, the exhibition opens on Wednesday and runs until September 3 2023.

The display will celebrate the newest stamp design with a unique chance to see a sheet of King Charles III 1st Class definitive before they are in public circulation.