Twelve years after ER concluded its 15-season run on NBC in 2009, the show's beloved cast — including stars George Clooney and Julianna Margulies — took a trip down memory lane and relieved their County General Hospital days.
On Thursday, the cast appeared in a live virtual reunion on Stars in the House to support costar Gloria Reuben's organization, Waterkeeper Alliance. The nonprofit aims to ensure that communities globally have clean water.
During the special Earth Day episode — which streamed exclusively on PEOPLE's social platforms — Noah Wyle revealed how Clooney, 59, helped to set the tone for the on-set environment.
"George, very early on, remember: you called us all to your trailer and you said, 'I've had the benefit of being on seven series that haven't bond. Here's what we're going to do differently. We're all going to be nice to everybody and we're going to erase the line between foreground and background and cast and crew, and we're all going to take our work seriously, but we're not going to take ourselves seriously. We're going to do our homework and we're not going to waste rehearsal learning our lines,'" said Wyle, who played John Carter.
Stars In The House
"You kind of laid out, you know, the ABCs of professionalism and that just became the standard that we operated under," he continued. "It should be standard operating procedure, but in a way, it was something that we kept our own counsel and were harsher on each other as castmates than anybody else above us was ever going to be. And we kept each other honest."
Clooney (Dr. Doug Ross) then teased his former costar by saying, "Noah, I think it's important you should know now — it's late, but you should know — we'd all met ahead of time and we decided that we had to have that conversation with you. That was an intervention!"
Sven Arnstein/NBCU George Clooney and Noah Wyle on ER
Jokes aside, the Academy Award winner noted that the cast was "really lucky" to have the work environment that they had. Clooney said that "every single actor that came on [the show] was treated with respect" and that executive producer John Wells "made a beautiful set."
Sven Arnstein/NBCU Cast of ER
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PEOPLE broke the news of Thursday's virtual gathering on April 13. At the time, Reuben — who played Jeanie Boulet — shared in a statement how "thrilled" she was to reunite with her former colleagues to support "a cause that is so close to my heart."
"I've been involved with Waterkeeper Alliance for 15 years, representing over 350 community-based Waterkeepers around the globe, and the work that they do is beyond comparison," the Canadian actress, 56, continued. "We must continue to fight for clean water not just on Earth Day, but all year round!"
Reuben later told Janine Rubenstein on the PEOPLE Every Day podcast that she "wrote letters" and "sent them out to my fellow castmates" to get them on board. "It's so beautifully overwhelming because it has been so long since I've seen these faces," she said.
ER aired from 1994 to 2009. Created by Michael Crichton, the Golden Globe and Emmy Award-winning drama followed the lives of the medical staff who worked at County General Hospital in Chicago.
In 2019, Wells suggested that the possibility of the series scoring a reboot isn't completely out the window.
"We made an awful lot of ERs, 331 episodes," he told Deadline that year. "That's a lot of hours, so I can't imagine that we would, but if somebody came in with a really interesting idea about how to do it, we might."
Getty Images Cast of ER
Speaking to PEOPLE for this week's issue, Margulies — who played Carol Hathaway for six seasons — revealed that her involvement on ER was initially intended to be much smaller.
"I was supposed to die," the actress, 54, said. "I was just a guest star. I had to drive my cranky little rental car to Crenshaw at this abandoned hospital."
The Good Wife alum also said that she considered Clooney, 59, to be her "mentor" on the series. "I followed and watched how he conducted himself on the set. When you create an environment that people feel safe in, then you do your best work. And George taught me that," she recalled.
"I felt so safe with him," she said. "I mean, I never thought, 'Well, why would I be in the bathtub and he's coming in?' I was like, 'Okay, I'll be in the bathtub. Yeah, great.'"