A photograph of the Queen and the Prince of Wales has been released to mark the end of her 90th birthday year.

The Queen and her eldest son were photographed in the White Drawing Room at Windsor Castle for the historic photo commemorating Her Majesty's milestone year.

The iconic image was taken by fashion photographer Nick Knight, who said he had wanted to capture the "warmth, humanity... strength and tradition" of the royal family.

Describing his experience of photographing the Queen - who last year became Britain's longest-reigning monarch - and the heir to the throne, Knight said: "It was a great pleasure and an honour to photograph Her Majesty The Queen and HRH The Prince of Wales at Windsor Castle."

The touching photo was shot before the final night of celebrations at the Royal Windsor Horse Show in May, BBC News reports. The tender moment between mother-and-son sees Prince Charles, wearing black tie, laughing after sharing a joke with the Queen. Her Majesty appears to be stifling laughter as she sits looking demurely at the camera with hands folded on her lap.

A Palace source told Mail Online: "It shows a real affection between them. There is a lot of good humour between mother and son. It is certainly expected to appear framed in one of the palaces before long."

The Queen celebrated her 90th birthday in April with a series of lavish events that included a private black tie banquet at Windsor Castle.

Queen Elizabeth's official birthday was marked in June with a service of thanksgiving with 10,000 guests and royal-watchers converging on The Mall for a picnic.

In a speech at the event, the Queen joked: "How I will feel if people are still singing Happy Birthday in December remains to be seen."

Earlier, The Queen and the most senior members of the royal family also posed for an historic photo ahead of the annual Diplomatic Reception at Buckingham Palace.

The image of the 'magnificent six', includes the Queen and her husband the Duke of Edinburgh, the heir to the throne Prince Charles with his wife, the Duchess of Cornwall, and the future King and Queen, the Duke and Duchess of Cambridge.