Prince and Princess Michael of Kent have been "betrayed" by the Queen and their position undermined, a damning magazine article claims.
The Kents have lost several perks
It says the couple have been denied many royal privileges, including the loss of their "grace and favour" London apartment within seven years.
The article, in next month's Tatler magazine, comes after last year's sustained media and political criticism that the couple allegedly did little in return for the luxury of living at Kensington Palace for a peppercorn rent.
Historian Andrew Roberts reveals the full extent of the Queen's moves to sideline the couple and keep them out of the high-profile position enjoyed by other royals.
The article suggests the couple were bullied by the Queen's senior advisers into accepting a "voluntary deal" last December where they would give up their Kensington Palace apartment.
The Kents were informed the Queen would pay their rent of £125,000 a year for seven years, after which they would have to leave their home, with no alternative accommodation offered.
It also reveals how the Kents have been left off the court circular, which lists their public engagements, leading to criticisms of laziness and poor value for money.
Mr Roberts says: "In reality, both the Prince and Princess have undertaken a heavy programme of public duties ever since their marriage.
"In the past four years, Prince Michael has carried out no fewer than 650 public engagements - more than the Dukes of Kent or Gloucester."
Both the Prince and Princess have undertaken a heavy programme of public duties ever since their marriage
The article suggests Prince Michael, the Queen's cousin, feels aggrieved that he is the only member of the royal family with the HRH title - other than his wife - not to have been offered an honorary military title.
"Even though he served in the army for 20 years and his father died on active service in the Second World War, he has been dropped from the wreath-laying ceremony at the cenotaph on Remembrance Day," says Mr Roberts.
However, the Queen's hard line did not end here, the article claims.
Mr Roberts says: "The latest humiliation came this year when Prince Michael was informed that he won't henceforth be receiving the same courtesies as other members of the royal family from British embassies abroad."
The historian makes a fierce attack on the Queen later in the article, claiming there was a deliberate campaign to move them out of Kensington Palace.
He says: "When the Kents posed the hypothetical question of whether they would be allowed to stay after 2009... they were told no.
"This proves that the palace campaign was not about saving money, but was intended to evict them."
Prince and Princess Michael of Kent are the only HRHs not on the civil list and this, says Mr Roberts, is down to "the religious bigotry of the 18th century".
The 1701 Act of Settlement - which is still in force - states that no-one married to a Catholic can accede to the throne.
"When Prince Michael married the Catholic Baroness Marie-Christine von Reibnitz, he lost his place in the line to the throne and any hope of being included on the civil list."
He reserves his strongest criticism for the closing paragraphs.
Queen is repeating history 'betraying' a cousin, says Roberts
He says: "The Windsors do not have a good record of helping their cousins in times of need.
"The Queen's grandfather, King George V, on the strong advice of his courtiers, reneged on an earlier promise to grant asylum to his cousin Tsar Nicholas II and his family after the outbreak of the revolution.
"This effectively ensured they were left to the mercy of the Bolsheviks.
"The way the Tsar's kinsman Prince Michael of Kent, and his family are being treated is the 21st century peacetime equivalent of that most callous betrayal."