A previously unseen photograph of a young Diana is causing a stir ahead of its US auction.

Pictured when she was around 18 and still Lady Diana Spencer, she is relaxing on a bed with a male friend on what's believed to be a ski holiday. A bottle of Johnnie Walker whisky stands beside them on a window ledge.

The contents of the photograph were seemed so controversial at the time, it carries a handwritten warning, "Not to be published".

The image was bought by the Daily Mirror in the early 80s, ahead of Diana's marriage to Prince Charles. However, the paper apparently decided not to risk upsetting Buckingham Palace by showing the future King's betrothed lounging around with a different young man - and a bottle of whisky to boot - and filed the 8 x 10 black and white snap.

The paper's archive was later sold and the picture made its way to RR Auctions in New Hampshire, which believes the photograph's handwritten, double-underlined instruction not to publish will see it exceed the average going rate of £750 when it goes under the hammer later this month.

Bobby Livingstone of RR Auctions told AFP: "It captures the moment when the engagement had been announced two days before and the press was going mad over Diana - but the Daily Mirror just wasn't going to publish this picture of her in a comfortable position with a man other than Prince Charles."

Words: Anna Pollitt. Pictures: RR Auctions/ Rex Features

Tweet us your thoughts on this rare picture of Diana, or post in the comments section below.