A former aide to the Prince of Wales has said the royal was at his “lowest” after the Princess of Wales was diagnosed with cancer.

In an interview with 60 Minutes Australia, Jason Knauf, formerly the chief executive of William and Kate’s Royal Foundation, said: “It was awful, absolutely awful. It’s the lowest I’ve ever seen him.

“Within a couple of weeks, if you’re Prince William, you find out that both your wife and your father have cancer. I couldn’t believe it.”

Both the King and the Princess of Wales were treated for cancer last year. Kate is now in remission and Charles is having ongoing treatment.

Mr Knauf, 43, stepped down from his position at the end of 2021.

Catherine’s diagnosis was made public in March last year, and Mr Knauf said: “The problem was that all this crazy conspiracy theory stuff kicked off in the background, online. ‘Was she really ill?’.

“But they didn’t want to say yet that she had cancer because they hadn’t told the children and they were still working through how to tell the children.”

Speaking to reporters last year at the end of his visit to South Africa, Prince William, 42, talked about how he has coped after both his wife and his father were diagnosed with cancer, describing the past year as the “hardest year” of his life.

“It’s been dreadful. It’s probably been the hardest year in my life. So, trying to get through everything else and keep everything on track has been really difficult,” he said after being asked how his year has been after a difficult year for the Royal Family.”

Mr Knauf also previously worked for the Duke and Duchess of Sussex.

In October 2018, while working for the couple as their communications secretary, Mr Knauf made a bullying complaint against Meghan.

He wrote of his concerns to William’s then private secretary in an email, in an apparent attempt to force Buckingham Palace to protect staff.

The duchess’s legal team strenuously denied the allegation.

Discussing William’s relationship with Harry, Mr Knauf said: “It’s very difficult to have this stuff play out in the public eye, but he’s chosen to keep his thoughts on it private, and I think all of us who know him really have to respect that we should do the same.

“But I will say, of course, it’s been hard and sad, especially for all of us who know both of them.

“I worked really closely with the two of them and we had lots of great times.”

Mr Knauf has previously expressed regret in not giving evidence in the Duchess of Sussex’s High Court case against the publisher of the Mail on Sunday, the Court of Appeal.

Meghan won her privacy case against Associated Newspapers Limited (ANL) in 2021, when the High Court found its publication of her letter to her father – sent in August 2018 – was unlawful.

Mr Knauf was made a Lieutenant of the Royal Victorian Order (RVO) in the 2023 New Year Honours List.

Before joining the royal household the American-born former corporate affairs executive worked for a range of institutions, from the office of the New Zealand prime minister to HM Treasury and the Royal Bank of Scotland.

Mr Knauf led a review of the Royal Foundation’s role and structure from March 2019, before becoming its chief executive in September of that year.

He oversaw the launch of the Foundation’s Earthshot Prize – William’s £50 million environmental prize, now an independent charity, which recognises solutions, ideas and technologies that “repair the planet”.