Princess Michael of Kent has described Princess Diana as "uneducated" and the older royals as "boring."
The 69-year-old, known as Princess Pushy, made the controversial comments during an interview with disgraced newspaper tycoon Conrad Black to promote her latest historical novel The Queen of Four Kingdoms.
While she began the interview insisting that she could not speak about the royals she quickly proffered her own assessment of the royals.
Speaking of the late Princess Diana she said: "She was my next door neighbour at Kensington Palace and I must say I was very fond of her, very attached to her. She had an enormous amount of goodness in her.
Princess Diana was working as nursery school teacher when her engagement to Prince Charles was first announced. She had left school with no O-levels and often bemoaned her lack of academic success.
"Like probably many people of little education who find themselves, like pop stars or film stars, suddenly lauded by the whole world, it is very difficult if you have not had a mother bringing you up who was quite stern and strict.
"She did not have a mother bring her up and she did not have much education, so it is much harder to cope with eulogy," she added.
Princess Michael went on to express her delight about the marriage of William and Kate Middleton and the arrival of the royal baby Prince George.
"Of course we're thrilled to have a beautiful young married couple with a baby. Let's hope there are more marriages soon because I think to have that young generation is terribly good for the people.
"The people love to see happy young people and I think the older generation are a bit boring for most people."
The Princess's glib comments have caused outrage in royal circles.
Royal biographer Lady Colin Campbell dismissed the remarks as 'rubbish'.
Ashley Walton, co-author of Prince Philip: Wise Words and Golden Gaffes, spoke in defence of the royals telling The Sunday Express: "Philip is 93 this year but he is anything but boring. In many ways he and the Queen are far more interesting than the younger royals because of what they have experienced in their long lives.'
The Princesses choice of interviewer might also be deemed to be somewhat suspect.
Conrad Black, the former owner of the Chicago Sun-Times was convicted of three counts of fraud and one count of obstruction of justice in a U.S. court in 2007 and sentenced to six and a half years' imprisonment.
In 2011, two of the charges were overturned on appeal, and he was released on May 4, 2012.
Princess Michael, a divorcee from Bohemia, married the Queen's cousin Prince Michael in 1978.