The 39-year-old star has revealed that she sustained the embarrassing injury as she shot risqué scenes with three different men in the Cold War-set Peacock drama.
Speaking to TheWrap, Clarke said: "Three men, in a number of hours. Just keep bringing it - I'm going to sit on this thing, you're going to bring them in, we're going to pretend to have sex. I broke a rib that day."
The Game of Thrones actress' co-star Haley Lu Richardson confirmed that the story was true.
The 30-year-old star said: "She really did. She's such a tiny little sensitive body, meant she broke a rib."
Clarke explained that she had to tell her doctor that the injury was as a result of "sex, times three!".
She added: "It didn't like, fully break. It just popped out a little bit."
Clarke rose to fame by playing Daenerys Targaryen in the HBO series Game of Thrones and revealed that she had a "full mental breakdown" when the show ended in 2019 - although she was thankful for the coronavirus pandemic as it gave her the chance to reflect on a turbulent decade that saw her suffer two brain haemorrhages and the loss of her father in 2016.
She told the New York Times newspaper: "It was the first time in my professional life that I stopped.
"I had a full mental breakdown. It was almost as if the timing of the pandemic was bang on...
"It forced me to answer some questions I probably could have put off answering for another 10 years...
"(During the show) there was never any time to stop and consider the meaning of it. I never had the foresight to think, 'You're going want to take a minute.'"
Clarke admits that she is unlikely to take on another role in the fantasy genre after starring in Game of Thrones.
The Last Christmas star said: "You're highly unlikely to see me get on a dragon, or even in the same frame as a dragon, ever again."
Clarke even explained that she was "hesitant" to accept a leading role in Ponies - which centres on two female CIA operatives investigating the deaths of their husbands - as she was concerned about the "commitment" it would require.
She said: "I was definitely, like, 'A lead in a TV show? I know what that commitment feels like.'"
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