The 14 original candid images are from the wedding reception at Buckingham Palace on July 29, 1981. None of the photos have ever been published and only very few people have ever laid eyes on them.
They originate from the collection of an assistant to English photographer Patrick Lichfield.
The present collection, consisting of seven black-and-white glossy photos and seven colour satin-finish photos, will go on sale at RR Auction in Boston on September 24.
Three show Princess Diana holding the five-year-old Clementine Hambro, her youngest bridesmaid; one shows her setting Clementine down; and another shows her smiling as Prince Andrew leans over to talk to Clementine.
More From This Section
Queen Elizabeth is clearly visible walking alongside Princess Diana in four of the images, and the Queen Mother is seen in two.
Prince Charles is also in two of these photographs. One striking photo depicts Princess Diana and Prince Charles from behind on the famous balcony overlooking the massive crowds gathered on the Mall in front of Buckingham Palace.
The first image pictures Princess Diana and Prince Charles standing beside one another, seemingly beaming with happiness and two show Queen Elizabeth watching a small television broadcasting images of the massive crowd outside.
One photo shows Princess Diana in the Throne Room as her dress designers Elizabeth and David Emanuel arrange the train in preparation for the formal photographs.
Another image depicts Princess Michael of Kent from behind in her turquoise dress and two show the Royal Family gathering for the formal photographs, with Mark Philips, Prince Andrew, Princess Diana, Prince Charles, Earl Spencer, the Duke and Duchess of York, and Baroness Fellows present.
Two years ago his company sold a pre-marriage photo of Diana with a male friend for USD 18,000.
"I think this collection will go for at least that price, personally I think more. In the States there is still great interest in Princess Diana," he said.