A former aide to the Prince of Wales said he was at his “lowest” after his wife Kate was diagnosed with cancer about a year ago.

Jason Knauf was chief executive of William and Kate’s Royal Foundation before stepping down at the end of 2021, and also previously worked for the Duke and Duchess of Sussex.

Both the King and the Princess of Wales were treated for cancer last year. Kate is in remission, while the King’s treatment continues.

“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,” Knauf has told 60 Minutes Australia in interview for an episode titled “Where There’s a Will”.

Describing a phone call with William about the princess’s diagnosis, which was made public in March last year, Knauf said: “It was awful, absolutely awful. It’s the lowest I’ve ever seen him.

“But 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.”

The prince also spoke about the twin diagnoses in November last year. In rare comments on a visit to South Africa, he said 2024 had been “the hardest year of my life”.

“Honestly? It’s been dreadful. It’s probably been the hardest year in my life,” William told the BBC.

“Trying to get through everything else and keep everything on track has been really difficult.

“But I’m so proud of my wife, I’m proud of my father, for handling the things that they have done. But from a personal family point of view, it’s been brutal.”

Knauf said what he used to talk about the “most” in the past with William was “how he and the princess were going to prepare their children for life in the public eye”.

“His childhood in front of the media was quite difficult at times, and he knew that he was going to be raising his kids to deal with social media and mobile phones and all of that stuff,” he said.

Knauf said William, the 42-year-old heir to the throne, would do things his own way when he did become king.

“Every generation of the royal family has to reinvent the role for the generation that they serve,” he said.

“The succession planning operation is a kind of always-on thing.

“The lessons, as much as they are, they don’t really look very much like what you might see in The Crown. This is about sort of private family conversations, learning by doing.”

In October 2018, while working for the William’s brother Prince Harry and his wife Meghan Markle as their communications secretary, Knauf made a bullying complaint against the duchess. He emailed his concerns to William’s then private secretary, in an apparent attempt to force Buckingham Palace to protect staff.

The duchess’s legal team strenuously denied the allegation.

“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,” Knauf said of William’s strained relationship with his brother.

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

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

-with AAP