Today I hit the set of 'Glee' to watch some fabulous ladies perform the show's big 300th musical number mash-up. (It's amazing, by the way ... more on that soon.)

Yes, it's just another big moment in a long line of milestones for the chart-topping show, but a quick Q&A with the cast and producers afterward revealed some very fun casting scoop, too.

Jonathan Groff, a.k.a. fan-favorite Jesse St. James, is returning to 'Glee' later this season -- but not in another glee club.

Executive producer Ryan Murphy revealed that Groff will be playing the new coach of rival club Vocal Adrenaline.

We last saw Groff's two-timing Jesse in the spring when he popped back into ex Rachel's (Lea Michele) life to make amends. We're sure those two will have an interesting reunion -- and if Michele is planning on sticking around McKinely post-graduation, maybe Rachel will be inspired by Jesse's new teaching gig -- but according to Murphy, it's 'Glee Project' runner-up Alex Newell who'll "have many scenes" with Groff.

Thoughts?