The growing scandal surrounding Andrew Mountbatten-Windsor could threaten the future of the monarchy itself, according to a British historian who says the crisis may ultimately end the reign of King Charles III.

Author and royal biographer Andrew Lownie, who wrote the unofficial biography Entitled, says the stakes extend far beyond the former prince – and hinge on what the King knew about his brother’s alleged misconduct while in public office.

“This is far more serious than the abdication crisis,” Lownie told ABC’s 7.30, referencing the 1936 abdication of Edward VIII, who stepped aside to marry American divorcee Wallis Simpson.

“It could bring down King Charles,” Lownie said. “The BBC put a series of questions to Charles … they refuse to answer quite sensible questions about what they knew. This is a real crisis, and they don’t seem to have woken up to the seriousness of it.”

Mountbatten-Windsor was recently arrested on suspicion of misconduct in public office, prompting the King to issue a statement backing a full investigation.

“I have learned with the deepest concern the news about Andrew Mountbatten-Windsor and suspicion of misconduct in public office,” the statement said. “What now follows is the full, fair and proper process by which this issue is investigated … Let me state clearly: the law must take its course.”

Despite that show of support, Lownie believes the monarchy’s predicament could worsen if it emerges the King was aware of the alleged conduct and failed to act.

“If the royal family knew about that and didn’t deal with Andrew, then the crisis is not just one about Andrew. It’s one about the king himself,” he said. “What people now want is complete honesty about what he knew, when he knew it and what he did about it.”

Authorities are investigating allegations that Mountbatten-Windsor leaked confidential information while serving as a UK trade envoy between 2001 and 2011, after retiring from the navy. Reports suggest emails show him attempting to promote the financial ventures of controversial businessman David Rowland.

“We’ve had emails published saying that he was warned about Andrew and his association with David Rowland,” Lownie said. “This was one of the people that Andrew was sharing confidential information with – and Charles did nothing about it, or appears to have done nothing.”

The latest investigation comes against the backdrop of years of controversy over Mountbatten-Windsor’s ties to Jeffrey Epstein. While he has never been arrested or charged over those associations, public sentiment shifted sharply after he was named in US court documents in 2015 by Virginia Giuffre.

Giuffre accused Epstein of forcing her to have sex with the royal when she was 17. She later filed a civil sexual assault lawsuit in 2022, which Mountbatten-Windsor settled while denying all allegations. Her posthumous memoir, released last year, further intensified scrutiny, alleging she was trafficked to the former prince.

“He was friendly enough, but still entitled – as if he believed having sex with me was his birthright,” Giuffre wrote.

Emails uncovered in the Epstein files also appear to show Mountbatten-Windsor sharing reports from official trips to China, Hong Kong, Singapore and Vietnam.

After nearly 11 hours of police questioning, Mountbatten-Windsor was released without charge but remains under investigation.

ABC royal commentator Juliet Rieden described the arrest as unprecedented.

“We are in uncharted waters – completely uncharted waters,” she said. “For a senior royal to be arrested, that has never happened in modern history. It’s incredibly damaging to the royal brand.”

Images: Wikimedia Commons, Department of the Prime Minister and Cabinet