David originally made the bizarre revelations in an article for Stellar Magazine.
Admitting that it was "the strangest column" he had ever written, he went on to say his young son had been insisting he "used to be the Princess" for the past year and a half.
"It started when someone gave my wife Lisa, who is very British, a thank-you card with Lady Di on it. Billy pointed and said, 'Look! It’s me when I was a princess,'" David admitted.
David, who shares three children with Lisa - nine-year-old Leo, and four-year-old twins, Billy and Betty - said his son's comments regarding Diana became more and more accurate, even though the couple have never shared any details of the Princess or royal family with their children.
Billy is said to have kept insisting he was Diana, and mentioned the "sons" he had "as a Princess."
Billy also left his parents speechless when he accurately described the royal family's Balmoral residence to a Scottish friend who was visiting the family.
"To a Scottish friend of ours, he claimed when he was Princess Diana he used to go to a castle in that kilted wonderland. He described the castle as having 'unicorns on it' and was called Balmoral," David shared.
The unicorn is a national animal of Scotland, and Balmoral is adorned with the mythical creatures.