The first Royal Mail stamps bearing the profile of King Charles III will go on general sale at post offices and retailers from Tuesday.
But while special presentation packs of the new design will be available, stamps featuring the image of Queen Elizabeth II will be sold first.
The mail service said the old stamps will continue to be on sale until stocks run out.
King Charles, who succeeded his mother to the throne in September last year, reportedly said he did not want the old stamps destroyed.
The format is the same as the first one featuring Queen Victoria which was first issued in 1840, except that the king is not seen wearing a crown as with previous monarchs.
The issuing of the new stamp comes a day after the price of first and second class stamps went up.