LONDON: Britain's Royal Mail is celebrating Prince William and Kate Middleton's wedding with a new set of stamps that feature their official engagement portraits.

Two pictures of the couple taken by fashion and celebrity photographer Mario Testino will be printed on the set of commemorative stamps, which can be ordered beginning April 7.

The Royal Mail said Tuesday the collectibles have been approved by William and will be released on April 21, the birthday of Queen Elizabeth II.

William has been featured on stamps twice before - to mark the Queen Mother's 100th birthday on August 4, 2000, and three years later to mark his 21st birthday.

Meanwhile, Transport for London said Tuesday that William and his bride-to-be will also grace special commemorative transit cards.