Now playing in London, you can see the critically-acclaimed Mary Stuart, starring Juliet Stevenson and Lia Williams. But you'll never know beforehand which actor is playing which part - they decide who will be Elizabeth I and Mary Stuart by the toss of a coin before the show.
Role-switching can keep a theatre show fresh and give the audience the excitement of never knowing what they'll see that night. Here are five theatre shows, in both London and on Broadway, which have switched up their leading roles.
1. Old Times
Photo Credit: Old Times
Kristin Scott-Thomas and Lia Williams traded roles nightly in Harold Pinter's Old Times, in 2013. Critics raved about the way the two actresses took on the roles of Anna and Kate and brought something new to each part.
Photo Credit: National Theatre
Taking on the monster and his maker, Benedict Cumberbatch and Jonny Lee Miller switched roles in Frankenstein at the National Theatre, directed by Danny Boyle. Fans of Sherlock in particular were keen to see Benedict take on the Monster, a far more physical and less cerebral role than they'd ever seen him in before, and also enjoyed catching Johnny's tortured Dr. Frankenstein, never knowing which one they'll see.
3. True West
Back in 1994, Michael Rudko and Mark Rylance switched roles as two brothers in Sam Shepard's play, True West. While the actors are switching parts, the characters themselves are also going through a role-reversal of their own as family tensions rise. When the play went to Broadway, John C. Reilly and Philip Seymour Hoffman took on the roles and also swapped throughout the run.
Photo Credit: MONIQUE CARBONI
At the start of Branden Jacobs-Jenkins's off-Broadway play Everybody, the casting of the lead role each night is decided by a lottery. The main character, called Everybody, faces Death who tells them they can bring with them a companion from life. Unfortunately, Everybody finds that neither Beauty, Friendship or even Stuff will go with him into the afterlife.
5. Romeo and Juliet
If you thought role-swapping was a recent idea, you may be surprised to hear that in 1935, Sir Laurence Olivier and Sir John Gielgud switched roles in Shakespeare's Romeo and Juliet. From October to November, the first month of the show's run, the two leading great actors played one role then switched for alternating periods of several weeks at a time. In the show's final week in 1936, Laurence played Mercutio with John as Romeo.