A royal expert claims Prince Harry "resents" the idea that Prince William is the "sensible" one.
Journalist and royal commentator Duncan Larcombe met Harry for a drink in 2008 after results of an inquest into Diana's death were published, according to the Daily Mail.
He told Ok! magazine that Harry had "unresolved anger" over his lack of control of his life and what was being said about his mother.
Harry has "never been able to shake his discomfort at not being 'normal'", as well as his anger over how he was portrayed in the media compared to his older brother, although he "often offered William advice".
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"'Harry was absolutely furious that his father's advisers had put out a statement. That was a sign to me that he has an inbuilt, unresolved anger about having no control of what's said. This desire to control his own destiny has always been there," Larcombe said.
"Harry has never been able to shake that resentment of not feeling normal either. It's a shame that no one has said to him, 'Your brother wants what's best for you.'
"Harry once told me that he really resents the perception that William's the sensible one while he's the loose cannon. He said there were times when it was actually Harry giving William advice."
New royal biography Finding Freedom promises to reveal details of the rumoured rift between the brothers. Will and Kate are currently living in Norfolk with their three children while Harry and Meghan are living in Los Angeles with their son Archie.
Rumours of the rift first came out when it was reported that William told Harry to "take things slowly" with his relationship with Meghan.
Royal writer called the brothers' broken relationship "just a very sad situation" and said the pair had "now gone their separate ways".