'Glee' is an unstoppable juggernaut, and it's showing no signs of slowing down. The series has collected guest stars left and right, but the show's biggest get could be Sir Paul McCartney.

Yes, that Paul McCartney, the former Beatle.

At an event honoring the series, 'Glee' co-creator Ryan Murphy told E! Online that McCartney has sent him a mixed CD.

"The other day a package arrived at my office and I opened it up and it said 'Mixtape From Paul McCartney,'" Murphy said. "It was very sweet ... It was a CD, I apologize. It was these amazing songs that I grew up with. And I said, 'Is this a joke?'"

Movieline pointed out that Murphy has hinted at a very big guest star for the show's post-Super Bowl episode, and McCartney certainly fits the bill. However, at this point McCartney's potential appearance is nothing more than a rumor.

So, which 'Glee' guest stars are confirmed to appear this season?

Murphy has confirmed (on more than one occasion) that 'Wicked' stars Kristin Chenoweth and Idina Menzel will be back this year, along with Lea Michele's 'Spring Awakening' costar Jonathan Groff. Murphy told E! that he's also trying to get Neil Patrick Harris back.

Javier Bardem's on-again/off-again rumored guest stint is back on, officially. Murphy told E! that Bardem will appear as a Spanish rocker in the later half of the second season.

Other confirmed season 2 guest stars include John Stamos as Emma's dentist/potential love interest, Cheyenne Jackson as the new Vocal Adrenaline coach, Charice as an exchange student rival of Rachel, Dot Jones as the new football coach and Chord Overstreet as Finn's protege who becomes his rival.

Tell us: Would you watch Paul McCartney on 'Glee'?