The actress read the part of the British monarch in The Audience, which focuses on the royal's hundreds of weekly meetings with the U.K.'s incumbent Prime Minister throughout her 60-year reign.
The performance was a private reading of the play in London, according to the Daily Mail. It is not yet known if the production will get a West End run.
A source tells the publication, ""It was rather poignant, seeing Helen as Her Majesty again.""
In 2007, Dame Helen won the Best Actress Oscar for her performance as the British monarch in The Queen.