The silence that followed was eventually broken by my elder brother snootily announcing, "I knew that." But I didn't, and at eight years old I was utterly shattered. I simply couldn't begin to make sense of it. "Didn't you even know, Jobby?" My eldest brother, using the sneering nickname by which he got under my skin, clearly sensed my shock. "I've always known," he+ added. My younger brother, at six, was reticent about being seen to be as candid as my tears began to reveal me to be, or as cocky as his eldest brother now boasted.
"Yes, darlings, I haven't had any hair since I was a girl," chimed my mother. "Your father was absolutely wonderful ever to marry me." So, I thought, this hairlessness had been a most terrible and unmentionable thing. And, curiously, right up until adult life it was to remain a most terrible and unmentionable thing."
The author is the Channel 4 news-reader Jon Snow. And the row he has provoked in writing a memoir of his boyhood relationship with his mother has been of the peculiar intensity which only a family spat can conjure.
Mrs Snow, it seems, suffered from alopecia totalis. At the age of 13 she lost her hair in a night while waiting to sit a piano exam. And that was that.
"But for me it wasn't," Snow recalls. "Very suddenly Mummy wasn't quite the same Mummy... I'd never for one moment wondered whether the hair on her head was real. I had taken it on absolute trust that it was. That it now wasn't, somehow undermined my entire confidence in who she was."
His elder brother Tom apparently remains the snooty fellow of the back seat. Instead of upbraiding his younger sibling direct he wrote a letter to The Guardian announcing that he was "shocked" to see that Jobby was blaming their mother for his inability to form close relationships. "She is severely ill with Alzheimer's disease," he wrote. "She is therefore, quite literally, defenceless in the face of such ghastly public retribution."
She developed the dementia after their father, a former Bishop of Whitby, died in retirement. She now lives in a nursing home in Oxfordshire where she has no idea her son is a television celebrity. "It is a horrible disease because she is still physically your mum. She sounds like her, but you can't have a conversation with her," he said of his visits every three weeks in an interview several years ago.
Yet there was always something curiously detached in their relationship, according to his essay in Sons and Mothers, which is to be published next week. While his brothers gravitated towards their father, who was a bishop and a do-it-yourself enthusiast, the boy Jon was drawn into his mother's orbit. His beautifully written lyrical account of those early years - in which he turned the pages of her piano music as the engagement ring on her long, slender fingers clicked on the ivory keys - is a haunting tale of a deep attraction that was somehow never resolved. His unsatisfied yearning for a closer relationship with the mother who called him the daughter she never had is unbearably poignant.
Physical closeness was what was lacking. "Nanny would wash our hair on Fridays and we would lie on towels in front of the fierce glowing elements of the old-fashioned gas fire in my mother's bedroom. These were the very rare occasions when we were allowed into her room. She would be there, too, sitting close by, sometimes assisting the drying with a towel. Beyond those treasured moments in front of the gas fire, I have no memory of any other tactile life with her. I did not sit on her lap, nor even run my fingers through her hair, as my children do mine. Kisses were an endurance - perfunctory, charged with nothing. And yet I was conscious of being the apple of her eye."
She found it hard to demonstrate emotionally. On his first day at Winchester choir school his mother left without saying goodbye. "In that instant the heart-broken, bereft but independent new me was born," he writes. "The umbilical was finally broken." She had also left him with a "pathological fear" of close relationships with women.
When her Alzheimer's deteriorated five years ago, to the point where she had to be moved into full-time care, he felt unable to take her into his own home. "Perhaps if our life together had prepared us and left us with a living friendship, I might have tried. But as it had not I was ruthless in my refusal to make sacrifices to care for her."
Brother Tom has no sympathy with the emotional charge his famous brother loads on his recollections. "I cannot see how anything in his childhood can now justify the humiliation of our mother, whose memory of those times has been wiped out," he wrote. "It is simply pitiless. Self-indulgence has gained the upper hand over decency."
Vehement disagreement seems of the essence in such matters. Sons and Mothers has been jointly edited by the critic Victoria Glendinning and her sportswriter son Matthew. They wrote pieces for the book about each other and managed to fall out in the process.
Matthew was horrified when his mother pushed the first draft of her contribution through his letterbox. "I thought, `Why are you writing all this down and not saying it to me?' ... It was so negative," he says. It took a month to sort out the anger. The experience of editing with her had been "extremely weird", he says, and it has definitely changed their relationship.
Quite what will be the impact on the Snow brothers is unclear. "I probably see my brothers only once or twice a year," Jon said in an interview published last year. "We are a pretty distant family. It's a great pity but you can't artificially engineer these things." Yet he apparently hopes that his brother won't find what he has written quite so abominable once he reads the whole book.
"It is not easy to tell the truth - the truth, that is, as one sees it, for there is no such thing as a single, whole truth," wrote Victoria Glendinning yesterday in response to the Snow furore. "It is all subjective. That is the tragedy of family life.
It is also the comedy and farce of family life." Which side of that coin eventually lands face-up for the Snow brothers remains to be seen. Perhaps they will decide it would be best to keep it in the family.
`Sons and Mothers', edited by Victoria and Matthew Glendinning, is published by Virago on 7 Nov at pounds 16.99.