(Image credit: Caren Archive)

The mystery of the young man sitting beside the late Diana Spencer in a photo apparently prohibited from being published has been solved.

The photo of Lady Diana before she married into the royal family will be up for auction later this month. Besides the identity of the mystery man, the words, "not to be published," written on the image in grease pencil, intrigued the photo's owner, Eric Caren of Caren Archive.

Caren had bought images from the former British newspaper, the Daily Mirror.

The man in the photo is Adam Russell, a student at Oxford University at the time and the great-grandson of former Prime Minister Stanley Baldwin. He is currently a deer farmer in Dorset, England.

Reached on the phone in western England, Russell confirmed with ABC News he was the man in the photo, but refused to say any more.

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Asked whether he had any additional photos of himself at the time, he replied, "you've got one, it was just several years ago… The hair's a bit shorter, otherwise you'd probably recognize [me]."

According to royal biographer Andrew Morton, the two were just friends.

In Morton's book, "Diana, Her True Story - In Her Own Words," he writes that her friend, Mary-Ann Stewart-Richardson, invited Diana to join her family on their skiing holiday in the French Alps. It was there that Lady Diana and Russell were injured and so they spent a lot of time together.

She fell on the ski slopes and tore all the tendons in her left ankle.

Morton said, Russell "always liked Diana but nothing ever happened, in part because he never expressed his desire for her."

Diana did not attend Oxford but the two apparently kept in touch when they returned to London.

"After the holiday, he went away for a year and when he came back he was told he had competition: the Prince of Wales," Morton said.