Rare photo of teenage Princess Diana up for auction

An intimate black-and-white photo showing a teenage Princess Diana is set to go up for auction later this month.

British media reports say the photo was possibly taken during a Swiss skiing holiday around 1979 or 1980, when the future Princess of Wales would have been 18 or 19 years old.

The image - which RR Auction says may have never been seen by the public -- shows Diana lying in bed, with a young man seated behind her and a bottle of Johnnie Walker sitting on a windowsill.

The words "Not to be published" are handwritten on the front of the photo. On the back, the photo is stamped Feb. 26, 1981 -- two days after her engagement to Charles, Prince of Wales.

According to the Daily Mail, that date is when the photo was sold to the Daily Mirror, which never published it. The Guardian adds that the Mirror's photographic archive was acquired seven years ago by the New York-based Caren Archive, which is now selling the photo through RR Auction of New Hampshire.

Bidding is set to begin on Jan. 17 at $200, and will conclude on Jan. 24.