If you haven’t seen it already, watch it now. Don’t miss it. If you don’t have a computer, see it on someone else’s. I was sent the link last week, without explanation, in a short e-mail from a friend, and idly double-clicked on it, imagining it was another of the internet jokes with which friends distract one another from working. In fact, this short video clip of a middle-aged spinster singing, posted on YouTube only a few days ago, is one of the most moving and astonishing things I have seen for months. It made me cry.

I’m not alone: the film star Demi Moore tweeted that it made her “teary”, and everyone I’ve shown it to has clearly been very moved, from girls in their early twenties to several late-middle-aged businessmen at a dinner party on Thursday. What I saw on their faces as they watched was incredulity and a dawning, I truly think, of joy. The public response is making internet history. By this weekend more than 25m people had hit YouTube to watch.

For the few people who don’t know about this clip, I should explain. To me, watching without any idea of what was coming, it was at first rather puzzling: an odd, dumpy, middle-aged woman, wearing an old-fashioned frock and unfashionably cut grey curls, is being interviewed, casually, in a busy TV studio by two patronising young media men. It quickly emerges that her name is Susan Boyle; she is nearly 48, unemployed and just about to sing on a huge stage in the Britain’s Got Talent show. There is something quaint about her manner, or, as people used to say, a bit simple, and something vulnerable too, as she keeps hitting slightly the wrong conversational note.

She reveals that she lives alone with her cat Pebbles and has never been married nor ever been kissed, with a strange, self-deprecating smile that I recognised in retrospect: it’s the secret smile of someone who has often been laughed at. But she is full of a surprising confidence. “I’m going to make that audience rock,” says this most unlikely person.

Anyone of any sympathy would at this point have felt sorry for her - sorry for her misguided confidence, sorry for her delusion that she could possibly hold her own performing in a talent contest and sorry about the growing obsession with celebrity among people who can only be hurt and disappointed by their immeasurable distance from it.

An unsympathetic person, by contrast, might have sneered slightly, but the derision and jeering contempt that actually met this poor woman, seconds later, when she appeared on stage was quite shockingly brutal, especially for these sentimental times. She might as well have been a martyr in a Roman arena. As she clumsily answered a few questions, and said she wanted to be like Elaine Paige, TV cameras filmed open contempt on the faces of the young audience and there were audible boos and jeers. Worse still, the judges were also laughing at her, Simon Cowell rolling his eyes in affected disbelief and Piers Morgan openly sneering. All this because a plain and middle-aged lady, the living antithesis of youth and cool, had the effrontery to enter a talent contest.

Yet Miss Boyle, with her strange serenity, seemed oddly untroubled. Then she began to sing, and after only two or three notes of I Dreamed a Dream from Les Misérables, it was absolutely obvious that she was a star. As one of the judges said later, and most revealingly, they knew at once that they had “found gold”. She has, without any doubt, a beautiful and powerful voice, and all the confidence, the authority, the self-discipline and the presence of a great performer; her talent transforms her. The judges and audience could not fail to recognise this and very soon they were standing and cheering rapturously, astonishment all over their faces.

What really interests me about the clip is not so much her talent as her story and people’s passionate reaction to it. Susan Boyle’s experience has all the symbolic power of a fairy story. It’s a story of transformation - always one of the most powerful - both for her and for her studio audience.

She, in fairy-story terms, is the ugly old lady, despised by all, who turns out to be a beloved and powerful princess; the spell that sets her free and makes her great is her magic talent. And the special magic of this talent is that it is makes no distinctions of age or beauty or disability; anyone might have this magic power, whether or not anyone else knows. Aspirations and dreams need not always grow old, though we must. It is a fairy story to make grown men and women weep, and it did.

Similarly, the jeering audience of vain young people trying to catch the camera’s eye and the preening judges of this contest are the nasty boys and girls of fairy stories who mock the poor old lady because she is not young and beautiful, only to be punished when her real self is revealed. And their punishment is to be revealed as they truly are - heartless, thoughtless and superficial - the flotsam and jetsam of the polluted seas of celebrity, likely to sink without trace into toxic foam. They will grow old too, to be ignored in their turn, and then they will understand that appearances are not everything. And those who despise people who are not thin, not young, not beautiful and not cool will one day find themselves despised in exactly the same way, by people just like their younger selves. That is enough to make young people think.

This side of the story became even more forceful for me when it emerged that Miss Boyle suffered mild brain damage at birth, causing problems that meant she was bullied and belittled at school. In retrospect I think that is enough to explain her slightly unusual manner, and the bullying and belittling sneers of the studio audience; it’s what they were laughing at. But Susan Boyle managed to rise above people like them. She found herself in church choirs and karaoke, restored and triumphant in music; it’s a story of the undefeated spirit.

Hers is also finally a story of the astonishing power of music to bring people together, transcending all differences. Everyone should sing. Everyone certainly can sing – there is almost no one who cannot learn to sing in tune. And the joy of singing in itself, or in a choir, is one of the best consolations I can think of for life’s sadnesses; I started singing lessons a couple of years ago and am amazed by what it has come to mean. As a nation, as individuals, we don’t sing enough. We should be inspired by the surprising Susan Boyle.

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