Boyle, of West Lothian, wowed the judges and crowd with her rendition of I Dreamed A Dream from Les Miserables during her audition in 2009.
The YouTube video of her audition has been viewed over 150 million times to date. Holden said the show has helped audiences to not “judge a book by its cover”. She added: “We still kind of do, to this day I thought Susan Boyle was going to be a stand-up comic.”
The popular ITV talent show returns this Saturday, against the final of BBC rival The Voice.