George Clooney’s ER Costar Julianna Margulies Emailed Him Before His Broadway Debut: ‘I’m So Proud of You’ (Exclusive)

Julianna Margulies has nothing but support for George Clooney ahead of his Broadway debut.

On Wednesday, Oct. 23, PEOPLE spoke exclusively to Margulies, 58, at the Broadway opening night of Left on Tenth, her new play costarring Peter Gallagher.

While at the event, held at the James Earl Jones Theater in New York, the Good Wife actress discussed how she and her former ER costar, 63, are both taking on Broadway. While Marguiles has starred on Broadway before, the upcoming stage production of Good Night, and Good Luck will mark Clooney’s first time on the Great White Way.

“No, I’ve just given him a lot of kudos,” Margulies tells PEOPLE when asked if she gave any advice to Clooney, who will take the stage in spring 2025. “I just emailed him and said, ‘I’m so proud of you. You don’t have to do this.’ ”

According to Margulies, in many ways, theater can be more challenging than acting on television.

“It’s scary, you know, being on Broadway. And the world we live in now, everyone’s a judge, and you have to block all that out and do your work,” she tells PEOPLE. “And so, I’m really proud of him for picking a hard road. It’s not easy work, and I’m really impressed that he’s doing it.

Margulies and Clooney have remained close friends since costarring on the medical drama, which debuted in 1994 and ran for 15 seasons before ending in 2009.

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In the series, she portrayed head nurse Carol Hathaway, while he played her love interest, Dr. Doug Ross.

While celebrating the show’s 30th anniversary in September, Margulies told the Television Academy that they still refer to each other by their character names.

“It always had to be Carol and Doug, in the end,” she said. “George and I, to this day, still sign our personal emails to each other ‘Love, Carol’ or ‘Doug.’ “

Margulies’ Broadway play is a romantic comedy by Delia Ephron based on her bestselling memoir of the same name.

Meanwhile, Clooney will make his Broadway debut in Good Night, and Good Luck — a play based on the 2005 film he co-wrote, directed and starred in.

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“A work of historical drama, Good Night, and Good Luck centers on a clash between famed journalist Murrow and infamous U.S. Senator Joseph McCarthy, of anti-communist HUAC fame. The title comes from Murrow’s broadcast sign-off. Clooney starred on screen as Murrow’s co-producer, Fred W. Friendly,” an official synopsis reads.

“I am honored, after all these years, to be coming back to the stage and especially to Broadway, the art form and the venue that every actor aspires to,” Clooney said after the play was announced in May.