Joanne King (born 20 April 1983 in Dublin) is an Irish actress. She is best known for her roles as Cyd (Cynthia Pyke) on the BBC1s Casualty and as Jane Boleyn, Viscountess Rochford in the Showtime 2007 - 2010 series The Tudors.
King is the second of four children, father Ronan is an accountant and mother Edel is a volunteer teacher. She attended St. Brigid's Girls School in Cabinteely and St Joseph of Cluny Killiney. She trained at the Gaiety School of Acting, Dublin.
She moved to London from Ireland to follow her dream of becoming an actress and was working as a BBC tour guide when she auditioned for a role on Casualty. She is most notable for playing the character Cyd (Cynthia Pyke) on Casualty. But it is her role as Anne Boleyn's sister-in-law, Lady Jane Rochford in Showtime's hugely successful show The Tudors which has brought her to international attention. Her character appeared first in the middle of Season Two in a small supporting role which was expanded for the fourth and final season which saw the downfall and execution of her character.