The black-and-white photo shows a teenage Diana on a Swiss ski holiday lounging on the lap of a young man, who has been identified as Adam Russell, the great-grandson of former prime minister Stanley Baldwin. He is reading a book and resting it on Diana's shoulder.
A bottle of liquor rests on a window ledge above her head, creating an image that was certain to be unfit for a future princess, and is one that was marked "not to be published," according to Britain's Daily Mirror, which purchased the picture in Feb. 26, 1981 – just two days after the then-Diana Spencer was engaged to Prince Charles.
The photo was kept hidden in the paper's archives until it was purchased seven years ago by the private Caren Archive. It is now set for auction by RR Auctions in New Hampshire, and is being described as a "salacious teenage image of the future princess."
"This would certainly not be in the way the Royal Family would have Diana to have been presented," said Eric Caren, owner of the Caren Archive, to the Daily Mail.
Diana is thought to be 18 or 19 years old when the photo was taken. It is expected to sell for at least $1,200 – though there are reports it could go for several thousands of dollars.
Diana, who rose to become an international fashion icon and human rights activist, and who later split with Prince Charles, died at 36 in 1997 in an infamous Paris car crash. Her tragic death sent Britain and the world into mourning as her two sons, Prince William and Prince Harry, were left without a mother.