The future king appears on a new postage stamp marking the 90th birthday of Queen Elizabeth
Credit: Ranald Mackechnie/Royal Mail

It’s the future King and the reigning Queen – or as they’re known to each other, George and Gan-Gan.

Holding onto the right hand of his dad Prince William, 2-year-old Prince George – standing tall on a stack of foam blocks – shows off a huge smile and the famous Cambridge cheeks in a shot taken last summer in the White Drawing Room at Buckingham Palace and released on Tuesday.

Photographed by Ranald Mackechnie, it is the first time George has appeared on a British stamp and was released in celebration of the Queen’s 90th birthday on April 21.

The sweet portrait features four generations of direct heirs: Queen Elizabeth, her son Prince Charles, his son Prince William and of course George.

(And yes, he’s wearing his signature knee socks – the very same ones available in PEOPLE Shop!)

The little royal had a little help to make sure he was roughly on the same “line” as the adults, with Mackechnie using high-density foam blocks to lift him into the frame.

The Royal Mail released the four first-class stamps (cost: 54 pence each, or 78 cents) on a single sheet, with perforations around the faces of the four royals.

There are also six special stamps that celebrate Queen’s birthday. Three focus on Her Majesty s family life, including one of her with her children and, for the first time a stamp with her father, King George VI.

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Another shows her as a young mother with Prince Charles and Princess Anne, while there is one with her husband of 68 years, Prince Philip.

The other three mark the Queen’s official role, showing her as Head of State for the opening of Parliament; as Head of the Commonwealth, where she is shown with the late South African president Nelson Mandela; and on a state visit to New Zealand.

The stamps are available to pre-order starting on April 20 at and available to buy from 8,000 Post Offices around the U.K. beginning on April 21.