Royal photographer Ian Pelham-Turner was granted seven minutes with the late Princess Diana, Prince Charles and their first-born son in 1982, but the candid snapshots were lost shortly after a selection were used in the British press.
The snapper gave up on ever finding the family shots he had taken - but they were discovered amid a haul of his photos in a Fleet Street basement in London.
He explains, "Recently I get a call from an agent to say he's found 10 boxes in the cellar of this building and can we come and pick them up or else they're gonna throw them in the skip (trash)."
"We find a space for them and we put them into storage."
And, in among the collection was one very special carrier bag full of celebrity shots.
Pelham-Turner adds, "My business partner tips open the bag and out falls Diana, out falls Prince William (pictures)."
The shots were unveiled as part of Pelham-Turner's appearance on U.S. news show Access Hollywood Live on Tuesday, and he admits they brought back great memories.
He explains, "In those days you weren't allowed to direct them (royal family) in any way, you weren't allowed to talk to them... They sat down on set and that was it. No interaction at all."
"There's a lackey with a stopwatch and as soon as they sat down, on went the stopwatch."
And he reveals Princess Diana and Prince Charles both competed to land the "front page" photo: "Who would get the front page photograph with the child? There was a lot of anxiety."
"I could see the look on Charles' face - not best pleased; so then he picks William up and puts him on his knee... and starts tickling the tummy of William... Who's gonna get the best baby smile wins the day."