The 45-year-old actress voiced her admiration for Clarke in an Instagram post Thursday after the 32-year-old star went public about surviving two brain aneurysms.
Headey and Clarke have co-starred as Cersei Lannister and Daenerys Targaryen on "Game of Thrones" for seven seasons.
The HBO series will return for an eighth and final season in April.
"It took me a while to know this woman (there are 64000 of us after all) Not until she spoke to me about her experience did I fully realize the warrior she truly is (MOD for real x209840000)," Headey wrote, referencing Daenerys' nickname Mother of Dragons.
"She does really great things for causes that deserve it. She's kind and determined and funny and aware. #Thursday's MVP ... Here's to @emilia_clarke," she said.
Clarke shared her story in an essay for The New Yorker published Wednesday.
She recalled having a subarachnoid hemorrhage, a life-threatening type of stroke, in February 2011, two months before "Game of Thrones" debuted.
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"If I was to live and avoid terrible deficits, I would have to have urgent surgery," the actress wrote.
"For the next three hours, surgeons went about repairing my brain. This would not be my last surgery, and it would not be the worst, I was twenty-four years old."
Clarke experienced aphasia, impaired language that affected her ability to communicate, after the procedure.
She was devastated by the possibility of not being able to act and contemplated suicide in her "worst moments."
"In my worst moments, I wanted to pull the plug. I asked the medical staff to let me die. My job -- my entire dream of what my life would be -- centered on language, on communication. Without that, I was lost," the star explained.
While in the hospital, Clarke learned she had a smaller aneurysm on the other side of her brain.
After completing Season 3, she required emergency surgery after a procedure to treat the aneurysm failed.
"The recovery was even more painful than it had been after the first surgery," the star recalled.
"I spent a month in the hospital again and, at certain points, I lost all hope. I couldn't look anyone in the eye. There was terrible anxiety, panic attacks."
Clarke said she's "now at a hundred percent" after healing beyond her "most unreasonable hopes."
She voiced her gratitude and said she's helped launch a charity, SameYou, to provide treatment to those recovering from brain injuries and stroke.
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