Known to most of the world as Hermione Granger, Emma Watson has signed up to co-star in the upcoming flick Napoleon and Betsy.

The movie details the love affairs between a young girl (Watson, 18) and the former emperor, Watson’s first leading film role outside the Harry Potter franchise. The movie begins in 1815, when Napoleon was exiled to St. Helena. It was during this time the former leader of France met Betsy, daughter William Balcombe (who owned the estate where Napoleon was held). The affair between the two lasted for three years.

Betsy was originally set to be played by Scarlett Johansson, but she left when it became apparent the part would call for a younger actress. Watson is currently in production on the set of Harry Potter and the Half-Blood Prince, and is scheduled to begin shooting Harry Potter and the Deathly Hallows early next year. Sometime in-between she’ll get pinned into her big costumes for Betsy, as the film is slated for a 2009 release.