And 'Glee' fans, I know you're curious.
Take a peek after the jump to see what Mercedes, Santana and another soon-to-be-ex-New Directions member are up to for the big number, which we won't see until the Nov. 15 episode...
Wearing black cocktail dresses and black heels with their hair swooped to the side in sleek low ponytails, Mercedes (Amber Riley), Santana (Naya Rivera) and Brittany (Heather Morris) -- yes, Brittany -- were joined by Sugar Motta (Vanessa Lengies) and three other girls from the rival glee group.
The song -- excuse me, songs -- of choice? A mash-up of Adele's hits 'Rumor Has It' and 'Someone Like You,' with Mercedes starting off in full 'Rumor' mode, then Santana chiming in with a little taste of the softer ballad. Brittany didn't get to bust out a solo moment, but just her presence with the rival club means some more big changes are coming soon.
Bonus: This fabulously catchy mash-up is already Adele-approved!
"Adele heard the track on Monday, and she loved it. She approved it personally, which is fantastic," said Rob Stringer, Chairman of Columbia Records, who releases all of 'Glee''s original music, and also (completely coincidentally, he promised) Adele's. "She's a big fan of the show, too."