"ALL The Glee Originals received invites today to be in our 100th episode! More to follow," Murphy tweeted Dec. 3.
The episode will feature ten fan-chosen "Glee" songs from previous episodes that will be re-mixed and performed by the current members of New Directions. Voting for the top ten songs is now closed.
Following Murphy's initial announcement, he tweeted that original cast members "Amber, Mark, Harry" and "Heather" will return — referring to original New Directions Amber Riley (Mercedes), Mark Salling (Puck), Harry Shum, Jr. (Mike) and Heather Morris (Brittany).
He also tweeted that Tony Award-winning actress Kristin Chenoweth, who guest starred on the series, will return. Chenoweth responded with a tweet that read, "Very excited."
For more on the series, visit Fox.com/Glee.