SHAME ON YOU, FERGIE; Duchess even shocks fun-loving Margaret.
The first hint to Fergie of the fury about to fall on her came as she had tea with the Queen at Windsor Castle.
During a lull in the conversation, she told the Duchess of York: "My sister isn't terribly happy with you."
Fergie knew better than to press for an explanation. But she was shocked and upset.
Even fun-loving Margaret, whose affair with Roddy Llewellyn made years of sensational headlines, had decided it was time to speak out.
A stinging letter from Margaret followed, accusing Fergie of bringing shame"on the royal family.
Last night, the duchess denied receiving the note, which was sparked by her toe-sucking affair with Texan John Bryan. But I can reveal details of the reprimand which left Fergie in tears. On March 19 last year the duchess and her children, Beatrice and Eugenie, were having tea with the Queen at Windsor Castle.
Nothing disturbed the informal chit-chat of the regular Sunday meeting - until the Queen mentioned Princess Margaret's fury.
The Queen does not like confrontations. And Fergie knew it was her way of saying: "I am not happy with you either but I am putting the complaint through a third party."
Next day, after a restless night, the duchess sent a note to "Dear Margo." She didn't apologise for anything, but sent good wishes and a large bouquet.
Days later, on Princess Eugenie's fifth birthday, Fergie received a hand- written reply from Princess Margaret's apartment at Kensington Palace.
Excitedly she ripped it open, expecting a "thank you" letter showing that any problems were now resolved. But the message was stark and uncompromising. Margaret, clearly referring to the pictures of the duchess having her toes sucked by John Bryan in the south of France, wrote: "You have done more to bring shame on the family than could ever have been imagined.
"Not once have you hung your head in embarrassment even for a minute after those disgraceful photographs.
"Clearly, you have never considered the damaged you are causing us all. How dare you discredit us like this and how dare you send me those flowers."
Last night a spokeswoman for Fergie said: "Neither myself nor Sarah have any knowledge of this letter. As far as we are concerned it never arrived.""
But I am satisfied that the story is true. There is now deep concern for the divorced duchess and her state of mind after two more tumultuous weeks in her already-devastated life.
The Queen has a soft spot for Fergie, although disapproving of much of what she does. And now the cover of her tell-all biography, Sarah The Duchess of York My Story, is set to cause more outrage - before a page is turned.
Fergie is pictured with her bare foot, famously caught on camera in the pictures with Bryan, on the book's front with her toe nails painted bright red.
In the wake of disclosures over his ex-wife's sex life and money troubles, Prince Andrew will attend a family summit about the future. On the agenda:
How Fergie might clear her escalating debts, now well over pounds 4million.
Where she is going to live.
Whether Beatrice, eight, and six-year-old Eugenie should remain so much under her control and influence.
Whether Andrew might leave the Navy even sooner than planned to exert more influence over the two princesses.
There is even talk of stripping Fergie of her Duchess of York title.
A royal aide told me yesterday: "We have gone beyond chronicling the number of the duchess's indiscretions. We are into a situation where we must monitor her moods carefully. She is very disturbed and we are under instructions to keep an eye on her."
Prince Andrew spent seven hours at Fergie's home on the exclusive Wentworth estate in Surrey yesterday.
He arrived at lunchtime in his Aston Martin and is believed to have had a long talk with his ex-wife about her future.