Gwyneth Paltrow is reportedly returning to Glee for the show's 100th episode.
The actress previously won an Emmy for her three-part appearance as substitute teacher Holly Holiday in 2011.
She will be reprising that role in Glee's two-part 100th episode airing in the US on March 18 and 25, according to the Hollywood Reporter.
Other guest stars expected to return for the special include previous series regulars Dianna Agron, Amber Riley, Mark Saling, Heather Morris, Harry Shum Jr and Kristen Chenoweth, who played McKinley High School graduate April Rhodes.
E! News reports former Gossip Girl star Chace Crawford will also make a special appearance.
"I think he's going to be Dianna Agron's new love interest," series star Matthew Morrison told the outlet.
"His name is Biff. He's kind of a Yalie degenerate."
It's unclear if Crawford will sing in the show.
Glee creator Ryan Murphy confirmed last year the programme's sixth season would be its last following former star Cory Monteith's sudden death in July.
The tragedy also forced Murphy's to rethink the show's original ending, which he shared with reporters in October.
In his original idea, Lea Michele's character Rachel Berry would return to Ohio from Broadway to find Finn Hudson as a teacher and running the Glee club.
"Rachel was going to have become a big Broadway star, the role she was born to play," Murphy told Entertainment Weekly. "Finn was going to have become a teacher, settled down happily in Ohio, at peace with his choice and no longer feeling like a Lima loser.
"Rachel comes back to Ohio, fulfilled and yet not, and walks into Finn's glee club," Murphy continued. "'What are you doing here?' he would ask. 'I'm home,' she would reply. Fade out. The End."