 Further arrangements were planned for when the couple would leave England and take up residence in Brittany as the recognised Duke and Duchess.However, within a few months, Mary developed "a lethargic disease from which it was impossible to rouse her" and she died sometime before 13 September 1361 without ever setting foot in Brittany.Her sister Margaret also died sometime after 1 October 1361, and they were both buried in Abingdon Abbey.