Prince William was at his "lowest" after his father and his wife were both diagnosed with cancer within weeks of each other

During an interview on TV show '60 Minutes Australia', Knauf explained: "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."

Princess Catherine recently revealed she's in remission while King Charles is continuing to receive treatment.

Knauf - who stepped down as chief ex ecutive of the couple's Royal Foundation in 2021 - went on to open up about how William and Catherine wanted to keep her diagnosis private until they had explained the situation to their children, but they were targeted by wild conspiracy theories online.

He 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."

William, 42, previously admitted 2024 was the "hardest year" of his life as his loved ones underwent cancer treatment.

During a visit to South Africa, he told reporters: "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 added: "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."