She not only helped develop the hit 1970s show, but also acted in it, and had a decades-long career in film, TV and theater.

Jean Marsh, the English actress known for starring in and co-creating "Upstairs, Downstairs" and appearing in films like "Willow" has died at age 90.

PEOPLE reached out to reps for Jean Marsh and Michael Lindsay-Hogg for additional information on April 13, but did not receive an immediate response. Marsh co-created the 1971 British TV series Upstairs,