Last Saturday, the unassuming 47-year-old left Simon Cowell and his fellow Britain's Got Talent judges slack-jawed with her performance of Les Misérables hit I Dreamed A Dream.
"This is the biggest surprise I've seen in all three years of this show," said judge Piers Morgan.
Now, Boyle is the most unlikely example of why shows like this exist - to create overnight sensations and international success stories out of everyday folk.
In less than 48 hours, the video of her performance stormed YouTube, and fan sites sprung up across the web.
When The Sun told of her worldwide YouTube success, Susan said: "Over a million? That’s incredible, it’s just fantastic.
"I can’t believe all of this, but I suppose it will sink in eventually. I had no idea the show was a worldwide thing.
"I never dreamed of reaching that many people. I am very flattered."
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