The soul singer, who had a hit with Super Duper Love, will play Anne of Cleves, the fourth wife of Henry VIII – who is played by Jonathan Rhys Meyers in the series, which is produced by Showtime in the US.
Joss will deliberately look unattractive for the role – Anne was only married to King Henry for about six months after she didn’t live up to his expectations in the looks department.
Anne was betrothed to the English monarch after Henry was shown a portrait of her.
But when she arrived in England, Henry was disappointed with her appearance, referring to her as the “Flanders mare”, and annulled the marriage in July 1540 after six months.
The latest season of The Tudors will follow the king as he weds Jane Seymour – played by Anita Briem – and then Anne of Cleves.
The costume drama made headlines with its first series for its explicit sex scenes, though it was panned by critics for containing little else in the way of substance.
Joss became a singing sensation aged just 15 but since moving to America has been looking to break into acting.
She appeared in the fantasy film Eragon in 2006, playing a witch, and recently starred in the Cadbury’s Flake adverts.