According to Janette Tough, 62, who performs as Wee Jimmy Krankie, one of Boyle's siblings was upset when she pretended to be the Britain's Got Talent star on stage.
Tough performed the skit, which involved her wearing a fat suit and pretending to have Boyle's pet cat Pebbles, with her husband Ian in Wolverhampton.
"Afterwards, I got a letter from Susan's sister. It said there had been enough of this mickey-taking of her sister and that it was disgusting," she told the Daily Record. "It said the trouble Susan had come across when she went to school was enough in her life.
"I wanted to write back and say, 'I was called the giant at school and it didn't affect me'. The world and her auntie were doing Susan Boyle in panto. The fat suit was a left-over from a French and Saunders sketch when I was Pamela Anderson.
"I thought it would be funny to have Ian rip off my Susan Boyle dress and have the fat suit underneath. I also pretended to have the cat Pebbles which 'peed' on the audience."
The veteran comic insisted that she has no hard feelings towards Boyle, adding: "I think she's smashing and good on her, she's done great. It's just the attitude of other people that annoys me. I'm sure Susan didn't mind."
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