Who was Princess Diana's mystery male friend? Previously unseen photo of royal as a teenager

She was the most photographed woman of her generation.

Which makes the emergence of an as yet unseen picture of a teenage Lady Diana Spencer particularly intriguing.

The mystery deepens, however, when it is revealed that efforts were made to ensure that the black and white photograph, taken on a skiing holiday before she met Prince Charles, never saw the light of day.

The picture is believed to have been taken on a Swiss ski holiday around 1979 or 1980 when Diana would have been aged 18 or 19.

It shows her lying on a bed in a chalet with a male friend, who is resting his book on her shoulder. On the window ledge behind them is a bottle of Johnnie Walker whisky.

The identity of the photographer is not known but the picture was sold to the Daily Mirror on February 26, 1981 – two days after Diana’s engagement to the Prince of Wales was announced.

It seems, however, that the picture editor of the day had second thoughts about publishing an image of the future Queen in an intimate pose with another man and scrawled across it: NOT TO BE PUBLISHED.

The picture remained in the paper’s archives until it was bought seven years ago by the private Caren Archive, which is now putting it up for sale through RR Auctions in New Hampshire.