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Prince brought Beyonce Knowles' sassy alter-ego Sasha Fierceto the forefront when the pop diva performed with him at the 2004 Grammy Awards.

Knowles family and friends insist Beyonce has always taken on a totally different persona when she gets on stage, but it took Prince to make her realise she 'trances out' and becomes Fierce during big shows.

Beyonce has since given the character a name and now uses her aggressive alter-ego to help her combat nerves and counter difficult interviews and photo shoots.

She even pays tribute to Fierce on her hit new album, I Am... Sasha Fierce.

She tells Giant magazine, "That night with Prince, I was just in a trance. I don't remember anything after I walked through the smoke onstage.

"I was definitely Sasha Fierce that night, completely free."

But the singer's parents first spotted Fierce when Beyonce was just six and performing at a school talent show.

Mum Tina Knowles explains, "She got on that stage and became a different person. My husband and I looked at each other like, 'Who is that?'"