"Much of the UK media will portray this eviction as a righteous act by a strong king.It’s anything but," said the BBC's former royal reporter.
He added,"Instead of building bridges the head of state is torching them.The banishment of his son is cruel, unnecessary and diminishes Charles."
The use of Frogmore Cottage was a wedding present from the late Queen Elizabeth II in 2018, and they refurbished it at a reported cost of £2.4 million ($2.9 million).
It has now been offered to Prince Andrew, King Charles III's disgraced brother, according to reports in The Sun and Daily Telegraph.
"We can confirm the Duke and Duchess of Sussex have been requested to vacate their residence at Frogmore Cottage," a spokesperson for the US-based couple said, without providing further details.
Harry and Meghan were reportedly told to vacate the property in January, just days after the publication of the prince's tell-all memoir "Spare".
Buckingham Palace declined to comment.
Harry's father Charles, who has long favoured a slimmed-down monarchy, has been undertaking an overhaul of family finances since his mother's death in September.
A possible axing of Andrew's annual grant of £250,000 a year could see him forced out of his current residence, the 30-room Royal Lodge, also on the Windsor estate, because of its huge upkeep costs.
Harry and Meghan's unofficial biographer Omid Scobie, quoting a source, wrote on Yahoo News that the couple had "until early summer to vacate".
"Initially they were given just weeks, but now they have at least until after the coronation" in May, Scobie wrote, adding that the couple had not yet heard if they will be invited to Charles's crowning.
Scobie also quoted a friend of the couple as saying, "it all feels very final and like a cruel punishment".
"It's like (the royal family) want to cut them out of the picture for good."
Harry and Meghan moved to California in 2020 after dramatically quitting royal life.
They have since taken part in a string of projects -- from an interview with Oprah Winfrey to a Netflix documentary -- airing grievances about their experiences as royals.
"Spare" smashed sales records when it was published in January, but also saw Harry's popularity ratings slump on both sides of the Atlantic.
Andrew, meanwhile, was forced out of public life over his friendship with the late convicted sex offender Jeffrey Epstein.
Last year, Andrew settled a US civil case for sexual assault with accuser Virginia Giuffre.
