Prince Philip thought Harry and Meghan Markle were wrong to quit their roles but supported his grandson's desire to "do his own thing", a long-time friend claims.
The Duke of Edinburgh thought Harry and Meghan's plan to become financially independent in the US while still supporting the Queen was "naive", said royal biographer Gyles Brandreth.
But Philip is reported to have accepted his grandson's decision and said "it's his life".
In the wake of Philip's death at 99 on Friday, Mr Brandreth has revealed what the duke really thought of Megxit, the Oprah Winfrey interview and Harry leaving his position as Captain General of the Royal Marines.
Mr Brandreth, 73, said Philip was sympathetic to Harry's distrust of the press and the duke loved his grandson and admired him for his service in the Army.
Harry, 36, has returned to the UK to attend Philip's funeral on Saturday, and is reportedly self-isolating at a cottage in the grounds of Kensington Palace, where his older brother Prince William, 38, lives.
Meghan, 39, will remain at home in Montecito, California, because, a Buckingham Palace spokesman said, she is pregnant and her doctor advised has her not to travel.
The duchess is due to give birth to a girl this summer.
Harry and Meghan stepped back as senior royals in March 2020 and settled in suburban Los Angeles with son Archie, who turns two in May. The pair have struck lucrative deals with Neflix and Spotify.
Megxit was finalised during a 12-month review in February when Buckingham Palace confirmed Harry and Meghan would not return as working royals.
The Queen stripped them of their royal patronages and Harry of his honorary military roles.
The Sussexes plunged the Royal Family into a fresh crisis in March when they made a number of explosive allegations during their televised interview with Ms Winfrey and discussed their rift with the Firm.
It was previously reported that Philip, who would have turned 100 in June, was shielding from the interview, which was shown while he was in hospital, and was "not aware" of the full extent of the couple's claims.
But Mr Brandreth, a TV presenter and former Tory MP, told the Daily Mail that Philip thought the interview was "madness" and nothing good would come of it.
On Megxit, Philip felt Harry and Meghan's decision to quit their royal duties and move abroad was "not the right thing, either for the country or for themselves", and thought their plans were "naive".
Mr Brandreth said the Duke of Edinburgh was "equally sorry" that "it should come to this", when the Queen, supported by Prince Charles and William, decided that the Sussexes would give up their official roles and not use their HRH titles for work.
Harry had taken over the role of Captain General of the Royal Marines from his grandfather in 2017.
Mr Brandreth said: "Philip had done the job for 64 years. Harry had barely managed 30 months.
"The Duke of Edinburgh was not pleased, nor did he believe that Harry and Meghan were doing the right thing either for the country or for themselves."
However, Philip supported Harry's desire to do "his own thing" on his own terms and thought him a "good man".
Mr Brandreth added: "He (Philip) said to me, 'People have got to lead their lives as they think best'."
The biographer said Philip did not want any involvement in the negotiations or last year's Sandringham Summit, where the terms of Harry and Meghan's departure were decided.
Philip is reported to have said of the rift: "I'll soon be out of it and not before time."
Harry will reunite with the Queen, Charles and William for the first time in more than a year when he attends Philip's televised funeral at St George's Chapel at Windsor Castle.
