An Aussie grandfather has shared photographs as part of his decades-long crusade to prove he is the secret love child of Prince Charles and Camilla.

Simon Dorante-Day, 55, who was born in the UK, claims that he was conceived in 1965. He says it’s this time when the successor to the British throne and Camilla were first romantically associated.

Prince Charles, Prince of Wales, has two sons, Prince William and Prince Harry, from his previous marriage to Princess Diana. Camilla, Duchess of Cornwall, also shares two children, Laura and Tom, with ex-husband Andrew Parker Bowles.

The future monarch couple does not have any children together, but British-born engineer Simon Dorante-Day, who settled in Australia after being adopted, claims that he is their biological child.

Simon, who says his middle name is Charles, was born in Gosport, Hamps, in April 1966. He also claims that Prince Charles and Camilla, who married in 2005, have ignored his letters to them.

Engineer Simon, who has fathered nine children himself, believes that the royal pair conceived him as teenagers when Charles was just 17-years-old and Camilla was 18-years-old, several years prior to when they are believed to have actually met in 1970 before he was adopted.

Simon was adopted by British couple Karen and David Day near Portsmouth in April 1966, when he was 18-months-old. He claims that his adoptive grandparents Winifred and Ernest worked as a cook and gardener for the Queen and Prince Philip.

He added that his adoptive grandparents help him to see Camilla until they had to stop because they were worried that he was going to remember the visits. He said they informed him multiple times that he was a royal son.

“I was walking to my nan’s (house) when I was about five or six and I heard nan say to mom,” he said. “Well, the visitations have got to stop, he’s going to remember them. I walked in the door and said, “Remember what?” and of course I copped a mouthful for talking out of turn.”

However, royal experts believe that Prince Charles and Camilla met each other in the 1970s, years after Simon was conceived.

When questioned about the conflict, Simon said ‘just because your grandmother said it doesn’t mean you are going to believe it.’

“I did do my research, so the timelines are gaps, people need to come forward and come clean,” Simon said. “I have a lot of evidence and I’m slowly collecting more.”

Simon has around 7,700 followers on his Facebook page and is supported by legal advisers and his wife Doctor Elvianna Dorante-Day.

He posted a comparison photo of the facial similarities between his 14-year-old son Liam and a young Queen Elizabeth.

“Ummmm, an interesting comparison,” the caption reads.

He also released “picture evidence” comparing photos of his son to photos of Prince Charles saying that it proves his link to royalty.

In 2016, Simon publicly declared to be Prince Charles and Camilla Parker’s secret son. He even filed papers to the High Court in a bid to force the Duke and Duchess of Cornwall to take a DNA test.

According to Simon, the related authorities have known about his appeal for more than 23 years but haven’t acted on it.

“I’ve said this before, but some people aren’t listening, so I’ll say it again!” he said. “I have a LEGAL right to pursue my True Identity – not to be lied to and deceived.”

“Firstly, the authorities (and by that, I mean Monarchy, Government, Health Departments, and Police) both in Australia and in the UK have been aware of my claims, and my issue, since at least 1998 when I first asked for my adoption paperwork. So, they know and have been across every detail, and all involved.”

Simon’s evidence includes memories of visiting Camilla at Broadlands House, where Prince Philip’s uncle lived at the time and having the “same bone structure as the Queen”.

He also claims that he was “made to undergo a procedure that changed his eye color from blue to brown” when he was eight years old.

In addition, he says that he was “pinned” down by a dentist as a child so his sharp canine teeth could be “ground flat” to remove similarities to the royals for the “cover-up”.

The Palace has never responded to Simon’s allegations, but he has not given up the fight.

“I’m always getting recognized,” he told 7NEWS AU. “I got photographed by another passenger on a train, on my way to Family Court. He was even videoing me at one point.”

“I’ve traveled all around the world and I’ve always had people stop me and say “Gee you look familiar” – without being able to put a finger on it,” he continued. “Some used to tell me point blank that I looked like a royal, without knowing my story. It’s been a common occurrence throughout my life.”

Simon told New Idea in 2019 that he believes his truth would never have been revealed if it wasn’t for the passing of Princess Diana in 1997. He also added that Princess Diana was preparing to reveal what Simon claims and that she knew it before her tragic demise.

“We believe that Diana knew of my existence and that she had put the pieces together, I think Diana was at a point where she was finding out answers about her life, how she was wronged, and she was going to go public with it,” he said.

“I’m simply a man looking for my biological parents, and every road has led me back to Camilla and Charles,” Simon added.