Groff, who can currently be seen on the HBO series "Looking," told ETonline, "I was there for the final shot and it was really emotional and celebratory…It was really special. I felt really lucky to be bearing witness to that. Those guys do an hour-long show for 22 episodes and they’ve been doing it for seven years. That’s a lot of hours clocked. So I think it was a really special moment for everybody."

In addition to Tony nominee Groff, the guest cast will also include Geraldo Rivera as himself; Andrew Rannells as himself; Mark Salling as Puck Puckerman; Kevin McHale as Artie Abrams; Amber Riley as Mercedes Jones; Jenna Ushkowitz as Tina Cohen-Chang; Jayma Mays as Emma Pillsbury; Dianna Agron as Quinn Fabray; Naya Rivera as Santana Lopez; Heather Morris as Brittany S. Pierce; Jessalyn Gilsig as Terri Schuester; Melissa Benoist as Marley Rose; Jacob Artist as Jake Puckerman; Alex Newell as Unique; and Blake Jenner as Ryder.

The series cast includes Lea Michele as Rachel Berry; Chris Colfer as Kurt Hummel; Darren Criss as Blaine Anderson; Chord Overstreet as Sam Evans; Jane Lynch as Sue; Matthew Morrison as Will; Dot-Marie Jones as Coach Beiste; Lauren Potter as Becky; Becca Tobin as Kitty Wilde; Laura Dreyfuss as Madison McCarthy; Billy Lewis Jr. as Mason McCarthy; Samantha Ware as Jane Hayward; Marshall Williams as Spencer Porter; Noah Guthrie as Roderick; and Iqbal Theba as Principal Figgins.