The beloved drama's biggest stars -- including Clooney, Julianna Margulies, Noah Wyle, Anthony Edwards, CCH Pounder and more -- came together for the benefit event, which raised money and awareness for the Waterkeeper Alliance, an organization that works to ensure every community worldwide has drinkable, fishable and swimmable water.
Stars in the House creators Seth Rudetsky and James Wesley hosted the reunion, and welcomed Gloria Reuben -- who portrayed physician assistant Jeanie Boulet on ER and serves as the President of Waterkeeper Alliance.
The group all reminisced like old besties and reflected on their on-screen and off-screen relationships, experiences with their unprecedented success, and how the show launched their careers.
Fans of the show tuned into the live event in massive numbers, and couldn't help but freak out over the chemistry that still existed between the former co-stars -- and how effortlessly charming and verbose Clooney was while celebrating all the talent around him.
Lol who needs hosts when you have George Clooney #ERREUNION
There are some shows I've rewatched many times and some that I was into for a moment in my life and haven't thought about since. ER is the latter (I'm not into medical shows, but I was into Noah Wyle and George Clooney), but it's exciting to see these people together again. pic.twitter.com/NETEMSsLy6
Two moments that stood out in particular for many fans were a story Clooney told about how the cast all flew out to New York City together to show their support for Edwards when he hosted Saturday Night Live in 1995. The whole cast also got tearful when Rudetsky and Wesley played an emotional clip from an episode featuring Clooney's aunt, famed singer Rosemary Clooney. Margulies, Wyle and Reuben all struggled to keep from openly crying after the tender scene.
ER, which revolved around the lives of doctors and nurses of Chicago's County General Hospital, debuted in 1994 and went off the air in 2009.
During Clooney's appearance last month on the SmartLess podcast with hosts Sean Hayes, Jason Bateman and Will Arnett, he revealed that his wife, Amal Clooney, has been watching re-runs of the iconic TV series. However, she's not impressed with his character, Dr. Ross, the hospital's resident ladies man and pediatrician.
"My wife is watching them now," he said. "And it's getting me in a lot of trouble because I'd forgotten all of the terrible things [his character Doug Ross] was doing picking up on women."