Julianna Margulies is celebrating George Clooney‘s major milestone! The 54-year-old actress took to Instagram on Thursday to wish her former “E.R.” co-star a happy 60th birthday.

In honor of the occasion, Margulies shared a throwback snap of her and Clooney hugging, which was taken while they were starring on the medical drama.

“Happy Birthday to my dear friend who reminded me yesterday that we have known each other for 27 years!” Margulies captioned the pic. “This picture was taken for the cover of TV Guide on the back lot at WB’s studios during a lunch break.”

Margulies also praised Clooney in her post, writing that he’s “a stand up fellow who walks the walk and reminds me all the time that doing the right thing is always the braver choice.”

In an April interview with People, Margulies opened up about meeting Clooney on the set of “E.R.”, on which she starred as Carol Hathaway for six seasons.

“He could not have been kinder or sweeter,” she said of Clooney, who played Dr. Doug Ross on the show’s first five seasons. “… 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.”

As they continued to work together on the medical drama, whose cast recently reunited for a charity event, Margulies revealed that Clooney became her mentor.

“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 said. “I felt so safe with him.”

As for how Clooney feels about entering a new decade, he recently told ET, “I’m not thrilled with it but it’s better than dead. So I’ll take it.”

More from ET:

George Clooney Reunites With ‘ER’ Cast and Fans Can’t Get Enough

Julianna Margulies Addresses ‘ER’ Backlash After Turning Down $27 Mil

George Clooney Says Wife Amal Isn’t Starstruck By His Role in ‘ER’

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