According to The Hollywood Reporter, Amanda Seyfried played Sarah, the eldest daughter of polygamist Bill (Bill Paxton) and Barb (Jeanne Tripplehorn) on the HBO series until the end of season four, when her character ran off with her husband Scott Quittman.
"Both Amanda and Paul really wanted to be a part of the last episode, even though they were both shooting movies," co-creator Will Scheffer told TV Guide.
The episode was shot in mid-December and will air in March.
Mark Olsen added, "It was special. Literally and figuratively it was a family getting back together."
Season five is set to premiere January 16.