The BBC's Antiques Roadshow surprised its viewers on Tuesday by revealing an unseen photograph of Princess Diana posing with her barefoot sons.

The photograph was presented to the program by the personal assistant of Lord Snowdon, the former husband of Princess Margaret.

Estimated at  £400 - £500 ($615 - $770,) the photograph shows Diana with a radiant smile and her two sons Harry and William, kneeling at her feet.

It really is fantastic. It's an odd one, because the boys are dressed in sort of country casuals and don't have any shoes on, and their nanny has not given them any socks as far as I can see. But the Princess of Wales is dressed up to kill, Antique expert Clive Farahar, told the Daily Telegraph.

Diana is glowing in the picture wearing a pink dress embroidered with gold intricate lace stitching. So Mum went out of something casual, slipped into something formal and got the boys in. I love the story behind that. It shows how unstuffy she was, Farahar added.

The photograph has not been released before and according to Lord Snowdon's personal assistant, the Royal archives do not even have a copy of it.

There were other photos presented from Snowdon's collection. One was of a formal picnic scene featuring Princess Diana, Prince Charles, Harry and William, but Farahar was far less impressed by this shot, saying it was too posed. Another black and white photograph showed Prince Harry in Princess Diana's arms, taken at the end of his christening.  

The picnic scene was valued at £200 to £300 and the christening picture at £500 to £800.

Lord Snowdon, now aged 82, was divorced from Princess Margaret in 1978 and from Lucy Lyndsay-Hogg in 2000.

Royal Dresses

Meanwhile, Princess Diana's royal dresses will go on display at The People's Princess' Exhibit at the Michigan International Women's Show in May, Patch reported.

Showgoers will see a replica of Princess Diana's wedding gown as they enter the show and the gown she wore dancing with John Travolta at a White House state dinner in the exhibit,  Beth Anderson, executive show manager of Southern Shows told Patch. The display has photographs and video covering a retrospective of her life as princess, mother, fashion icon and humanitarian.

The exhibition will tell the story of Diana's life through the possessions she auctioned off to charity. Informational panels will also be held as a part of the show between May 3-6.

The exhibit will be spilt into different sections, according to Patch:

1.       Entrance: A 15 minute introductory documentary tells Diana's story.

2.       Diana's Childhood: Diana's ancestral background, early childhood experiences and lineage that factored into her future relationship with Britain's Royal Family.

3.       Engagement and Wedding: A video story of the engagement announcement and Royal wedding, which was viewed by more than 750 million people worldwide.

4.       A Princess of Style & Charity: Video, graphics, sketches, notes and commentary from Diana's favorite fashion designers tell the story of Diana's legendary transformation from ingénue to style icon.

5.       The Servant Princess: The story of Diana's tireless approach to her duties as a princess with purpose as she ascended to global humanitarian, highlighted by the perspectives of those who benefitted from her compassion and generous use of her royal platform.

6.       Goodbye England's Rose-The Painful Passing of The Princess: Video of her brother's eulogy as well as the Royal Family's reaction to her death and ultimate honoring of her life. Guests can leave words of endearment and tokens if they wish.

7.       Finale Royal Dresses: Five dresses from Diana's wardrobe will be on display, including three by one of Diana's favorite designers, Catherine Walker: