On the hour-long finale, set to air May 9 from 9-10 PM ET, Duke and Baxter will play a longtime lesbian couple. Blaine Anderson, played on the series by Darren Criss, will encounter Duke's character at a jewelry store, where he is shopping for an engagement ring for Kurt (Chris Colfer).
Duke originated the role of Helen Keller on Broadway in The Miracle Worker and later reprised her role on screen in 1962, earning the Academy Award for her performance. She has also been seen on Broadway in Isle of Children and Oklahoma!
Baxter is an Emmy Award nominee for her work on "Family," "A Woman Scorned: The Betty Broderick Story" and "CBS Schoolbreak Special."
For performance highlights from this season's recent episodes, click here.