The veteran star picked up the Best Actress Academy Award for her role as Elizabeth in 2006 picture The Queen.
Mirren admits she was first inspired to sign up to the role when she saw a short film which showed the monarch as a 12-year-old girl - and the vision of the youngster already enslaved by her royal duties still makes the actress feel emotional.
She says, "She's getting out of one of those enormous black cars. She'd obviously been told you get out and you put your hand out and you are polite to the man who will greet you. But she's doing it with such gravity and grace and dignity as a 12 year old, and it makes me cry every time I look at it. It's beautiful."