Gerard Boyle told the Sunday Mirror that the 47-year-old – who has won fans across the world with her sensational performance on the ITV1 talent show – that as a teenager she would sing along to Osmond for hours on end, and knew his most famous song Puppy Love off by heart.
He also revealed that Susan was a fan of the hit musical Grease and would play the film’s soundtrack repeatedly.
“Susan was what you would call a loner,” Gerard told the paper. “She was happiest on her own, playing her records and losing herself in music. She didn’t really interact with other children.”
He said that as a teenager Susan – who was born with minor brain damage and targeted by school bullies because of it – retreated into her room with her record player to escape the outside world.
“She was easily upset,” Gerard said. “She’d take nasty comments literally so found it hard to make friends or develop relationships outside the family.
“Eventually she retreated into her own world. Music became her thing. When she was a girl she was obsessed with Donny Osmond.
“His posters were all over her walls. She would lock herself in her room and play the records over and over again singing along as loud as possible.
“It used to drive me mad when I would hear it start up the hundredth time. But our mum would say, ‘Leave her alone, it’s all she’s got’.”
Meanwhile, The Sunday Mirror reports that Susan – who said on last week’s Britain’s Got Talent that she has never been kissed – has finally had her first snog.
Friend William McDonald did the honours at a local hotel in Susan’s hometown of Blackburn, West Lothian – but says he doesn’t expect anything to come of their kiss.
“If there’s a lady to be kissed, I’m your man,” the divorced 64-year-old said. “But she’ll be looking for a younger fella now she’s world famous.”