The photograph might never have been seen publicly until now, RR Auction said.
Stamped February 1981 on the back, the photo was taken around the time Charles, the Prince of Wales, and Lady Diana Spencer ended months of speculation and announced they were to be married.
The photo came from the Caren Archive, a major private collection of rare newspapers and other publications, and was purchased seven years ago from the Daily Mirror newspaper.
In 1981, Diana first told news of her engagement to her friends, then moved out of her apartment on 23 February and into Buckingham Palace. What was widely labelled the wedding of the century took place on 29 July 1981, at St Paul's Cathedral in London. Their marriage ended in divorce in 1996, and Diana died in a Paris car crash in 1997.
Another Diana photo to be included in the auction is an original 1988 news photo of the princess observing a marriage conflict resolution seminar.
The auction is scheduled for 17-24 January in Amherst.
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