The King’s uncrowned profile, in silver and facing to the right, features on a collection of 10 first-class stamps with some of the nation’s favourite flowers.
But unlike Queen Elizabeth II's famous silhouette, the King is not depicted wearing a laurel wreath.
Among the chosen flowers for the new set is the sweet pea, one of the late Queen's favourite blooms.
The national flower of Ukraine, the sunflower, which has become a symbol of solidarity with the war-torn country, was also selected.
Other flowers in the first-class set include a purple iris, a pink lily, a fuchsia, an orange-red tulip, a dark pink peony, a bright orange nasturtium, a pale pink rose and a light purple-tinted dahlia.
Royal Mail said King Charles’ debut was a significant milestone in British philatelic history.
David Gold, director of external affairs and policy for Royal Mail, said: “Britain is a nation of gardeners, and a love of flowers runs deep in our collective consciousness.
“His Majesty is known to be a passionate gardener and we are delighted that the first special stamps to feature his silhouette should be a celebration of some of the most popular flowers in British gardens.”
The late Queen's silhouette, bearing her laurel wreath, has been a feature on Britain’s stamps since 1966.
An updated design was used from 1968, adapted from Mary Gillick's original cameo portrait of the monarch used on coins.
The final set to use the Queen's image was unveiled in February in honour of the 100th anniversary of the Flying Scotsman steam locomotive.
A Royal Mail spokesperson said: "Flowers mark our celebrations, our joys and our sorrows and, above all, they unify us through a pleasure that we can all understand."
The definitive stamps, used as regular issue day-to-day postage marks in the UK, go on sale in April.
A presentation pack containing the full set of special floral stamps will be available from March 23 and are priced at £10.40.