From Diana's sweeping train to the couple's kiss on the balcony, there's probably not one photograph from the iconic 1981 wedding you haven't seen.

But that was until now.

Over a dozen unpublished, behind the scenes pictures from Princess Diana and Prince Charles' London nuptials have been revealed before they're sold at an auction in Boston next month.

One image shows Diana clutching five-year-old Clementine Hambro, her youngest bridesmaid, in her arms. Others show the Princess' dress being arranged in the Throne Room for the official portraits and the Queen watching coverage of the wedding on a television.

“I was the only informal photographer allowed at the wedding of Prince Charles and Princess Diana,” wrote the unnamed photographer who is only identified as an assistant to the official wedding snapper Lord Patrick Lichfield.

“We were assigned by the royal couple, to take informal and formal photographs of all royal family and their invited guests after the ceremony when they returned to Buckingham Palace for the wedding reception. These were the photographs that were not used in the family album...to my knowledge none of them have ever been published. Very few people have ever laid eyes on them.”

“The black and white ones were printed by me, in the dark room in Aubrey Walk, within hours of the wedding,” he added in a note that accompanies the 18 photos which can be bidded on at RR Auction from 17 to 24 September.

An estimated 750 million people around the world tuned in to watch the royal wedding of Prince Charles and Lady Diana Spencer held at St Paul's Cathedral on 19 July 1981. A further 600,000 people filled the streets of London to catch a glimpse of the newlyweds. Princess Diana personally selected David and Elizabeth Emanuel to design her dramatic gown. The design duo described it as a dress that “had to be something that was going to go down in history, but also something that Diana loved” and which would be “suitably dramatic in order to make an impression”. It certainly did...

Take a look at the rare and heartwarming snaps from one of the most iconic weddings below.

Feast your eyes on these rare, unseen photos from Princess Diana's wedding