Princes George, William and Charles photographed with the Queen for special, birthday stamps

Six stamps issued by the Royal Mail to mark the 90th birthday of Queen Elizabeth II. Picure: PA

The young future king - who has his blond hair in a side parting and is wearing a smart white Rachel Riley shirt with blue piping - is seen grinning broadly in the head shot on the first class stamp.

The image of the Duke and Duchess of Cambridge's two-year-old son was captured by photographer Ranald Mackechnie as part of a specially commissioned wider portrait featuring four generations of the House of Windsor - the Queen and three future monarchs.

George - who will one day have his own profile as the silhouette on stamps - was pictured with his great-grandmother Elizabeth II, grandfather the Prince of Wales and father William in ornate white drawing room at Buckingham Palace.

In the touching portrait, which was taken in the summer of 2015, George is holding William's hand as he stands between the Duke and Queen.

The group family photograph appears as a stamp sheet - with perforations positioned to create a first class stamp for each of the four royals.

Behind the scenes, London based photographer Mackechnie had the challenge of ensuring the royals' heads were all roughly the same height for technical reasons - but toddler George was too short when stood next to his seated relatives.

Mackechnie came up with a clever solution - the Prince is actually balancing on four high density foam blocks, stacked together and secured by tape.

Mr Mackechnie, 55, described the royals as 'amazingly relaxed' and said George's joy and energy was fantastic.

'It's great just to be asked to photograph a stamp, never mind four generations of the royal family. When I was asked about I was ecstatic but I had to keep schtum for 18 months,' he said.

'The joy and energy coming out of George was fantastic. It lifted the whole shot and lifted the afternoon. He was on top form. He was quite fascinated by the lights. He took it all in his stride.'

He described how as soon as the royal family taken their seats for the portrait his computer crashed, but that he was able to use one of his spare ones which he had on standby.

The stamps have been unveiled on the day the Queen visits a Royal Mail delivery office in Windsor, beginning her public birthday celebrations ahead of her actual 90th tomorrow.

The visit also marks the 500th anniversary of the postal service and the Queen will be presented with a collection of stamps released over the years to mark her achievements - as well as the new ones of the monarch, Charles, William and George.

Six further stamps have been released for the head of state's 90th birthday - three focusing on the Queen's family life and three honouring her official role.