London: Actress Dame Helen Mirren admits portraying Queen Elizabeth on stage will be a "challenge" because the role spans 60 years of the monarch`s life.
The 67-year-old, who has previously played the monarch in hit movie `The Queen`, is to star in `The Audience` in London`s West End next year.
"That`ll be a challenge," femalefirst.co.uk quoted Mirren as saying.
However, she thinks the monarch`s "unbelievable consistency in everything" will help with the transition, and she is also studying the changes in her speech patterns.
"Her voice has changed and I can use that - she had a terribly posh voice when she was young. But now even the queen, while she isn`t quite dropping the ends of her lines - though her grandsons do - there`s a tiny bit of estuary creeping in there," she said.
"I can use all that to signify the age range and we`ll come up with other things," she added.