Queenslander, 49, claims royal couple are his real Mum and Dad.
A man living in Queensland believes he is the secret love-child of Prince Charles and Camilla, Duchess of Cornwall, he told New Idea and Seven News' Sunrise.
Simon Dorante-Day, now 49, was born in Gosport, Portsmouth, in England and adopted at 18 months by locals Karen and David Day.
He believes Camilla fell pregnant in 1965 but kept her pregnancy a secret.
The gap between birth and adoption was explained to New Idea by his Australian wife, Elvianna, with whom he has nine children.
"We believe that Camilla fell pregnant to Charles and that Camilla, with the help of her family and the royals, kept Simon until he was 18 months old," she said.
It has been reported the adoptive grandparents worked for the Queen and Prince Phillip in an unknown royal household. In the interview this week with the magazine, Dorante-Day said his grandmother Winifred told him "many times" he was Camilla and Charles' child.
"I was very close to my grandmother and she told me many times that I was Camilla and Charles' child," he said.
However, in the interview aired on Sunrise on Thursday morning, he said this information was revealed when his grandmother was on her deathbed.
"The last time I saw her, before she passed, was in hospital in Portsmouth. There was a newspaper on the bed, it had a picture of Charles and Camilla on it. I said to her, 'Is it these two?' and I pointed to them and she said, 'Yeah'," he said.
He told New Idea: "I know it sounds unbelievable, but anything I say is checkable.
"I'm simply a man looking for my biological parents and every road has led me back to Camilla and Charles."
Simon Dorante-Day. (left).
Dorante-Day said he remembers spending time with a young, blonde woman and being taken to homes in the Portsmouth area.
He believes Camilla fell pregnant to Charles in 1965, but she kept her pregnancy a secret as she "promptly disappeared from the social scene".
Dorante-Day told New Idea he will continue to fight to obtain medical evidence of his true lineage.
In his search for answers, Simon has written to many high-ranking officials in Australia and the UK, including Prince Charles himself, asking for DNA tests.
Despite being largely ignored, Simon refuses to give up.
"I've hired Australian lawyers to act in the UK and I'm going to fight it in their legal system,' he said.
