ET was at the exuberant celebration, where stars Debra Messing and Megan Mullally snipped the red ribbon as a confetti cannon sprayed the cast, before Sean Hayes and Eric McCormack sealed the deal with a passionate stage kiss.
Addressing the crowd, McCormick explained, "I was just saying to my wife, 'I wonder what it will be like to kiss a man again,'" when Hayes took the cue and grabbed McCormick for a wild, aggressive make-out session.
"It's just like riding a bike," McCormick quipped after the kiss.
"I always thought about the four of us as being like an orchestra, and each of us playing a different instrument and creating a musicality together," she shared. "When we started playing the music again, it was like, 'Oh!'"
According to Mullally, "none of us would have ever thought that we'd be doing this show again, because it's literally never happened before. We would have no reason to think, 'Oh, I'm sure that Will & Grace will just come back one day.'"
The cast commemorated their first day of filming with a slew of sweet Instagram snapshots, sharing selfies with their co-stars and photos from set.