After her mother died, a heartbroken Susan Boyle lost her voice – and almost missed the big break that made her a worldwide singing sensation.

The stunning secret is revealed in the blockbuster new book about the spinster from Scotland, Susan Boyle: Dreams Can Come True, by Alice Montgomery.

"Susan’s father died in 1999, and her mother Bridget passed in 2007 following a long illness. Susan had dedicated her life to caring for her mother, and she was so depressed that she lost her voice for a time," a publishing source familiar with the book told The ENQUIRER.

"Susan is quoted in the book, ‘For a while after my mother’s death, I wasn’t able to sing. I was too upset. I stayed at home, did the housework, day-to-day tasks.’"

But knowing how much joy her voice brought to her mother encouraged Susan to keep sharing her talent.

She eventually auditioned for the reality TV show Britain’s Got Talent, and the book recounts how the audience went wild over her electrifying performance.

But the episode didn’t air until five months later, and on the biggest night of her life, the 48-year-old spinster suffered from aching loneliness, according to the book.

While Susan felt euphoric, Montgomery writes that "she had no one to share those feelings with. Instead, she returned home alone…where only Pebbles [her cat] was waiting to keep her company," according to the source.

Susan herself confessed in an interview: "I was on such a high…Anyway, I turned the key in the door and I walked in to silence. There was nobody to tell, so I gave my cat Pebbles a cuddle, fed her, went upstairs, hung my dress up and just went to bed."

Her life has changed dramatically since then – with her "Britain’s Got Talent" audition attracting more than 300 million views on YouTube, and sales of her album, "I Dreamed a Dream," topping eight million copies worldwide.

While Susan is still a single, self-proclaimed virgin: "She’s had plenty of offers from men," said the source.

"She said, ‘I’m flattered and delighted by the attention.’"