Tom Bradby says Prince William and Prince Harry have been arguing for a year and a half.
The journalist - who was previously friends with both princes - claims the Duke of Cambridge and his brother the Duke of Sussex have been at odds for the past 18 months and it has made reporting on the royals much more difficult.
Tom - who conducted William and Duchess Catherine's 2010 engagement interview and presented an ITV documentary with Harry and Duchess Meghan in 2019 - told The Times newspaper: "Well, it used to be quite a straightforward thing, right, because they weren't arguing and life was simple.
"And then it just slowly descended into something that was difficult - personally and publicly - really over the past year and a half."
Tom, 54, also revealed he knew Meghan and Harry were "struggling" with royal life because he had been through his own mental health battle in 2018.
He said: "I was clearly influenced by my own experience and I didn't think they were in great shape, and so I altered the way I was planning to do the documentary."
He added: "I felt like there was an untold story" so he asked Meghan the question: "Are you OK?" which led to her revelation about life in the royal family.
She said: "Not many people have asked if I'm okay. It's a very real thing to go through behind the scenes…it has really been a struggle."
And Harry, 36, confirmed his feud with his brother in the documentary, saying they were "on different paths at the moment".
It was previously claimed that Tom and William, 38, are no longer close after William felt "betrayed" by his support for Harry.
A source told the Daily Mail: "William is a sensitive soul and believes it's in times of crisis when you find out who your true friends are. It would be fair to say Bradby hasn't been one of them."
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