Princess Diana and Prince Charles' wedding, if you recall, was one of the most-watched events. And now, a dozen of rare, candid, unpublished and behind-the-scenes photos of the royal wedding will go under the hammer in US.

US-based website RR Auction is planning to sell a batch consisting of 14 never-before-seen original photographs taken at the wedding reception held at the Buckingham Palace on 29, July, 1981, and wedding ceremony at St Paul's Cathedral.

 Click Here to view the photos.

The collection features six photos of Princess Diana in her voluminous wedding dress with members of Spencer family, as well as royals including Princess Anne (Charles' sister), Princess Margaret (the queen's sister), Queen Elizabeth the Queen Mother, and Prince Andrew (Charles' brother and best man).

Then, there are three that show Diana holding her youngest bridesmaid, five-year-old Clementine Hambro. Other photos include Queen Elizabeth walking along with Princess Diana, Diana and Charles on the famous balcony overlooking a massive crowds gathered in front of the Buckingham Palace.

According to Remarkable Rarities Auction (RR Auction), the intimate pictures of the royals relaxing and having fun at the ceremony were clicked by Lord Patrick Lichfield, who was the only photographer allowed to take informal photographs of the royal family and guests.

The website said that the photos never made it to the official wedding album, were never made public and have been kept in a private album for decades. These will now be sold for an estimate of $1,000 to $2,000 on thee website by an unnamed female photographic assistant to Lichfield.

The website has also published the letter of provenance, which read: "I was the photographic assistant to Lord Patrick Lichfield...the only photographer allowed to take informal photographs of the royal family and their guests when they returned to Buckingham Palace...for the wedding reception. These are original prints. The black and white ones were printed by me, in the dark room in Aubrey Walk, within hours of the wedding. The colour photographs were printed by a trusted laboratory that did the Lichfield studio colour work. Lord Lichfield had me make up an album of black and white and colour photographs, which he presented to Prince Charles and Princess Diana to commemorate the day of their wedding. These are photos that did not go into that album [and were given to Litchfield's assistant in recognition of the work done on the wedding photographs]. To my knowledge, none have ever been published. Very few people have ever laid eyes on them." An exceptional assemblage of never-before-released images from the 'wedding of the century.'

The live auction on RR Auction's website is scheduled for 24 September, 2015.