I'm Prince William's secret aunt...now I want the truth about my mother's upstairs-downstairs affair; Lord's Love Letters Hidden In Songbooks Reveal The Astonishing Romance That Could Send Shock Waves Through The Royal Family.
She claims she is the love child of Diana's grandfather Lord Fermoy, who took details of his illicit affair with her mother to his grave.
He feared a scandal if the truth ever emerged about his upstairs-downstairs affair.
But documents suggest that Lord Fermoy had a romance with married amateur actress Evelyn Rudderforth during World War Two which resulted in the birth of a girl.
The extraordinary details of the love affair have come to light only recently after 50-year-old letters were found by their daughter Ann Ukrainetz, who never suspected that Evelyn's husband Charlie was not her real father.
Shocked Ann, 55, was going through the personal effects of her late mother when she found love letters from Lord Fermoy hidden in dusty music hall programmes from the days when Evelyn appeared on the stage in Kings Lynn, Norfolk.
The most shocking letter of all was a handwritten personal message to Ann from her mother, which was hidden in an old song- book.
In the letter, Evelyn confesses that Ann is the daughter of Lord Fermoy.
She wrote: "My dearest, darling Ann, I know one day you will have this book in your possession, maybe after I have passed from this world.
"Please try to understand. I just have to get this off my chest. Charlie was not your biological father. I fell in love with Lord Fermoy and we had you as a result. He was married and I was just a commoner. There was nothing we could do. We stayed in close touch and he loved you very much."
The confession - along with handwritten romantic notes said to be from Lord Fermoy to Evelyn speaking of his love for her and their daughter - will rock his aristocratic relatives and the Royal Family.
It means that Ann is the half-sister of Princess Diana's mother, Frances Shand Kydd, and therefore would have been Diana's aunt. It also means she is a long-lost great aunt of young Princes William and Harry.
Yesterday mother-of-three Ann, who now lives in San Diego, California, and is divorced from her wealthy businessman husband, said: "I only discovered the truth earlier this year.
"It was an enormous shock. I'd always imagined she was devoted to the man I knew as Dad. Thank God he never knew about her philandering. He died in ignorant bliss.''
Her father Charles Rudderforth died in 1966. It is not known if Lord Fermoy's wife Lady Ruth knew, who died in 1993, knew of the affair.
The love letters were passed on to Ann when her mother died, also in 1996, and the 50-year-old secret literally tumbled out of the brown, musty pages. In her letter to Ann, Evelyn revealed how Lord Fermoy had been able to snatch moments with his illegitimate daughter without anyone discovering the truth.
"Remember we went to a lot of functions?" wrote Evelyn. "This was so your father could see you without creating a scandal. I wanted you to know because this makes you a `lady'.
"I wanted to tell you so much in person, but I lacked the courage."
At the time of the affair, Evelyn lived with Charles in Kings Lynn and Lord Fermoy and Lady Ruth lived with their daughters Frances and Mary at the family home Park House, on the nearby Royal estate at Sandringham. They also had a son Edmund, who later died.
It appears that Lord Fermoy used the local police superintendent, Fred Calvert, to deliver handwritten love letters to Evelyn at her home in Tennyson Avenue. Fred's wife Alice was also in on the secret.
The letters reveal handsome Lord Fermoy's passionate feelings for Evelyn, who he would call "my rose'' or "my flower''.
They describe how he would regularly send pounds 200 to help pay for Ann's singing and dancing lessons - but he never publicly acknowledged her as his own because of the scandal.
In one letter to Evelyn, Lord Fermoy allegedly wrote: "I am so sorry the birth of our Ann caused you so much pain. I feel it too. Alice will bring my flowers to you, my love. She told me how hard you had to struggle.
"I love you so very much. Don't worry, my Rose, I will take care of you always."
In another letter he wrote: "We have to be so careful my flower. Ruth is not well today and I cannot get away so I'm leaving your money with Fred, so he can once again deliver it to you. He has been so marvellous in keeping our secret.
"You looked so beautiful last night. I wanted so much to hold you again.
"I do so wish I could see Ann more often but it's impossible, there would be such a scandal. Ruth sometimes looks at me in a puzzling way. I wonder sometimes if she knows."
Lord Fermoy would often arrange for Fred and Alice to bring little Ann to Park House so she could play with his own daughters. During one visit Ann was even introduced to Princess Margaret, who was visiting the Sandringham estate.
Ann recalls: "He was a very nice man - but all I knew at the time was that he was a friend of Mummy's. There wasn't the vaguest hint that we were related."
Dashing Lord Fermoy, who was born in 1885, had a reputation as being a ladies' man and moved to Kings Lynn after growing up in the United States.
He lived in America because his father, the third Baron Fermoy, insisted on it as one of the conditions of inheriting the family title, which was created in 1855.
In World War One Lord Fermoy fought in France, but when his father died in 1920 he overturned the conditions in court and came to England.
He became firm friends with the then Duke of York (later George VI) and was granted the lease of Park House in the grounds of Sandringham.
One of the most eligible bachelors in the country, he had several lovers before he married Ruth Gill in Bieldside, near Aberdeen.
He is believed to have fathered Ann when he returned from France early in 1943, where he organised mobile canteens for the troops.
Ann, who now lives a millionaire's lifestyle in San Diego, in a house complete with its own aircraft hangar, said: "I get the clear impression they had been lovers for some time.
"I wasn't the result of an overnight quickie. My mother was an intense and disciplined person. She would never have allowed anyone - even an aristocrat - to have taken loose advantage of her in this way.
"She often accompanied me as a child to see Lord Fermoy at his big house. I have distinct memories of them being close friends. He would kiss her on the cheek and hold her hand.
"Of course, the significance meant nothing to me at the time." Lord Fermoy died in 1955, a month after he collapsed in a Kings Lynn hairdressing salon.
A year earlier, his daughter Frances married Diana's father and future Earl Edward John Spencer at Westminster Abbey and they moved into Park House, where Diana spent much of her early life. In 1956 Lady Fermoy was appointed by the Queen Mother as an Extra Woman of the Bedchamber.
She became one of the Queen Mother's closest friends and it was widely suggested that they acted as matchmakers for Diana and Prince Charles.
Shortly after Lord Fermoy's death, Ann and her family emigrated to Canada. She was 12 years old.
She said: "I was upset at leaving my friends behind at St James School and the thought of missing out on the posh parties I used to attend at Lord Fermoy's.
"I went to Sandringham at least two or three times a year. And I always had nice clothes.
"I never questioned where the money came from, any more than who paid for my piano and ballet lessons..but looking back now it doesn't take the brains of Einstein to work it out.
"I was always the best dressed kid on the street.''
The family settled in Ontario and Evelyn worked as a book-keeper while Charles was a labourer. After Charles died in 1966 Evelyn remarried, but within two years she was widowed again.
Ann has contacted Lord Fermoy's two daughters, Frances Shand Kydd and Mary Roche, to tell them about her existence, but her letters have gone unanswered.
She has even contacted Diana's brother Charles Spencer, but has had no reply.
She said: "Clearly the idea of a black sheep like myself knocking on their door must give them cause for concern."
But Ann is not looking for money and has not been paid by the Sunday Mirror. She says that all she wants is for the truth of her birth to be acknowledged.
"I don't want their money or a fancy title," she says. "I just want to know more about the man who was my biological father. I have no wish to exploit them.
"But I would like to be rightfully acknowledged as the daughter of Lord Maurice Fermoy even though I was born on the wrong side of the blanket.
"All I ask is that they show me a little decency and a modicum of respect as a long-lost relative."
Yesterday Lord Fermoy's grandson and the current holder of the title said: "I received a letter from this woman.
"The nature of her claims are not something I have given much consideration to.
"Until anything further comes out I'm not going to believe what she has to say."