(Image credit: Caren Archive)

A photo showing a rare glimpse into the life of Lady Diana before she married into the royal family will be up for auction later this month.

The photo formerly belonged to the former British newspaper, the Daily Mirror. It has the words, "not to be published" written on it in grease pencil, commonly used by photo editors. Diana appears to be lying in a bed with a male seated behind her. A bottle of Johnnie Walker Whisky is on the window sill next to her.

In Photos: Rare Diana Photo and Other Expensive Items

The date, Feb. 26, 1981, is written on the back side of the photo. Caren Archive, the photo's current owner, bought part of the photo library of the Daily Mirror.

On Feb. 23 of that year, Diana moved into Buckingham Palace, at just 19 years old. The next day, the palace had made an official statement about the engagement.

She married Charles, Prince of Wales, on July 29, 1981 at St. Paul's Cathedral.

The photo will be auctioned as part of a photography sale by RR Auctions of Amherst, N.H., from Jan. 17 to 24.

Eric Caren, the owner of Caren Archive, said he does not know who the man in the photo is for sure, though many have suggested the man is Diana's brother, Charles Spencer.

"If it is her brother, it is more curious why they squashed it," Caren said of the Daily Mirror's editors. "It's not an unflattering shot. It's a more intimate shot."

Bob Livingston of RR Auctions said the Daily Mirror was likely uncomfortable publishing a photo of the future Princess of Wales appearing to be in the arms of another man. He told the Daily Telegraph a similar photo could be sold for $1,000 but because of the words, "not to be published" on it, he expects it to be sold at a much higher price.

Also to be auctioned are a 1988 news photograph of Princess Diana observing a marriage conflict resolution seminar, an original photo of the Beatles playing in the 1960s and a studio portrait of Albert Einstein.