Royal biographer Penny Junor claimed Harry’s highly personal statement in which he criticised the media for a “ruthless campaign” against his wife would make his ongoing relationship with the press “quite awkward”.
“It’s (a) statement that I found very extraordinary and I think probably very ill judged,” said Ms Junor, who has written several books about the royal family, including the duke.
“None of the advisers that I’ve known over the years in any of the palaces would have let, in my view, a statement like that go out."
She added: “I can’t think the Queen would approve of that statement, I don’t think the Prince of Wales would ever put a statement out like that and my goodness over the years he’s had cause when the media have been attacking him or Camilla.
“I don’t think even his brother would have advised putting out a statement like that.”
Ms Junor said she understood Meghan’s decision to take legal action against the Mail on Sunday if she felt her privacy was breached and expressed sympathy for her husband.
“I like him a lot and I respect him and I feel very sorry for him because he is wanting to protect his wife and that’s really admirable and I think that he’s gone a bit over the top here,” she said.
But Ms Junor rejected Harry’s claims that the media were pursuing a wholly negative campaign against him and his wife.
She said: “I really don’t believe that there has been a ruthless campaign to do down Meghan, I think there have been some negative stories undoubtedly.
“They’ve not only been in the Mail on Sunday, they’ve been all over the press and I think some of the stories have been based in truth.”
As an example, she highlighted criticism of the royal couple’s use of private jets despite speaking out on environmental issues.
She also cited the couple’s decision not to make details of their son Archie’s christening public.
“They are all sorts of stories that have not played out well for them but the criticism has not been unwarranted,” Ms Junor said.
But she said the couple’s recent successful tour of southern Africa had “absolutely reset the dial” of press coverage for the pair.
Ms Junor said: “They have been doing what the royal family do best, going out and about being ambassadors for this country abroad, interacting with damaged children and communities that need support and help.
“That is absolutely the bread and butter of the royal family and what we love them for.”
Asked how the duke’s recent statement might affect his relationship with the press, Ms Junor said: “I think that going forward it might be quite awkward.”
She said the duke was “poking the bear” with his “very over-emotional outburst” and “might regret it”.
She added: “I feel the media will feel pretty bruised and hurt by what he has said because these are people who have followed him and written really lovely things about him over the years and I think they probably feel they’ve had a kick in the teeth.”