Photographs taken behind the scenes at the royal wedding of Prince Charles and Diana are to be auctioned, BBC News reports.

The set of 12 photographs were taken at the wedding reception in Buckingham Palace on 29 July 1981, which followed the ceremony at St Paul's Cathedral.

Six of the images show the princess with members of her family and the wedding party, including the Queen.

The photos come from the collection of an assistant to the English photographer Patrick Lichfield, the BBC says.

Lord Lichfield, the Queen's first cousin once removed, was the only photographer allowed to take informal images of the royal family and their guests when they returned to Buckingham Palace.

The collection, due to be auctioned in America next month, is accompanied by a letter of provenance from the assistant to Lord Lichfield, which identifies the people in each photograph and offers further details.

The Remarkable Rarities live auction event from RR Auction will be held in Boston, Massachusetts, on September 24, 2015, according to the BBC.

Auction spokesman Bobby Livingston said: "These never-before-seen photographs capture the candid and unrehearsed moments of the fairytale wedding."