Julianna Margulies Admits She and George Clooney Had a 'Crush on Each Other' During 'ER'

Julianna Margulies had no idea just how much her life would change after being cast in NBC's hit medical drama ER in 1994.

Margulies, who went on to play nurse Carol Hathaway for six seasons, still vividly recalls shooting the pilot episode. "I was supposed to die," she tells PEOPLE in this week's issue. "I was just a guest star. I had to drive my cranky little rental car to Crenshaw at this abandoned hospital."

Detailing her tumultuous childhood and journey to Hollywood in her new memoir, Sunshine Girl: An Unexpected Life, the actress, 54, who married attorney Keith Lieberthal, 48, in 2007, also remembers meeting one very handsome costar that day in the makeup trailer. "And he could not have been kinder or sweeter," she says.

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The chemistry that erupted between Margulies and actor George Clooney turned them into one of TV's hottest on-screen couples. "That can't happen if you don't have a crush on each other," Margulies allows. "And with George and me, it was so organic. I was just supposed to be a guest star, number 39 on the call sheet. But he treated everyone the same."

Margulies also insists Clooney, 59, became her "mentor" during the production. "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 says. "I felt so safe with him. 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.'"

Fans will finally get to see Margulies and Clooney together again — along with Gloria Reuben, Noah Wyle, Laura Innes, Anthony Edwards and more — on Thursday, during a live ER cast virtual reunion on the daily series Stars in the House, which will stream exclusively on PEOPLE's social platforms.

Airing on Earth Day, the special episode will be held in benefit of the Waterkeeper Alliance — the fastest growing global nonprofit focused solely on clean water.

"I think I'm just as excited as the fans are to see them all," says Margulies of the reunion, noting she regularly keeps in touch with Wyle, Clooney and Eriq La Salle as well. "In fact, I literally just was emailing with George because I said, 'I've written this book and you're in it, and it's not a tell-all, it's just that I have to give credit where credit is due and you should have it. And where do I send it, under what name and what country?'"

The actress also sent copies to Wyle and La Salle. "I just said, 'Listen, you guys are part of this trajectory of this incredible life, and you're my history and so I'd like to send you the book," she says.

"Everyone's been so responsive and kind and loving, and it's overwhelming to be honest with you," adds the actress, who has most recently been shooting Apple TV+'s The Morning Show in L.A.. "They'll be my other family for the rest of my life for sure."

Margulies' memoir, Sunshine Girl: An Unexpected Life, will be released on May 4.