Stone is to play Anne of Cleves, British King Henry VIII's fourth wife. Irish actor Jonathan Rhys Meyers plays a young, handsome incarnation of the famous 16th century monarch in the acclaimed series.
Showtime said Stone will star in three episodes, which are currently shooting in Dublin, Ireland. The show is to return to television in 2009.
"The new season will pick up after Anne Boleyn's beheading, detailing Henry's doomed marriages to true love Jane Seymour and the German-born Anne of Cleves," the network said.