For eight seasons on Game of Thrones, Emilia Clarke battled Dothraki, ice zombies, and Lannisters as the warrior queen Daenerys Targaryen. But unbeknownst to her fans and colleagues, the actress was also fighting a private battle: During her time on the show, she suffered two life-threatening brain aneurysms, which necessitated multiple surgeries and punishing recoveries. Clarke kept her health issues a secret until shortly before the premiere of Thrones’ final season, when she penned a widely acclaimed essay for The New Yorker detailing her fight for her health. In this excerpt from his new book, Fire Cannot Kill a Dragon: Game of Thrones and the Official Untold Story of the Epic Series, author James Hibberd reveals how Clarke kept working on the series while recovering from brain surgery.

Clarke wouldn’t reveal the real reason behind her exhaustion for another eight years. After filming Thrones season one, she had suffered a brain hemorrhage at a gym in London. “I immediately felt as though an elastic band were squeezing my brain,” Clarke wrote in The New Yorker. As she was rushed to the hospital, Clarke recalled lines of Daenerys Targaryen’s dialogue to try to calm herself. The actress underwent emergency surgery and for several days couldn’t even remember her own name, let alone speeches in Dothraki.

Somehow, just weeks later, Clarke returned to work on Thrones, despite still having a second growth on her brain that a doctor said might — in theory, though it was unlikely — “pop at any time.” Day after day on set, Clarke’s performance gave no indication of her fatigue, fear, and pain.

EMILIA CLARKE (Daenerys Targaryen): It was crazy intense. We are in the desert in a quarry in like 90-degree heat, and I had the consistent fear that I was going to have another brain hemorrhage. I spent a lot of time just being like: “Am I gonna die? Is that gonna happen on set? Because that would be really inconvenient.” And with any kind of brain injury, it leaves you with a fatigue that’s indescribable. I was trying so hard to keep it under wraps.

BRYAN COGMAN (co–executive producer): Only a very select few people knew about that. I was completely unaware. I heard a little bit that she had some problems between seasons, but nothing to that extent. And I had no clue while we were shooting.

ALAN TAYLOR (director): We were afraid for her. She’s so brave, because it never affected her commitment to the work.

EMILIA CLARKE: If I had called my doctor, he would have been like, “Dude, you just need to chill out.” But I still felt blind fear, and the fear was making me panic, and the panic was leading me to feel like I’m going to pass out in the desert. So they brought in an air-conditioned car for me — sorry, planet.

DAN WEISS (showrunner): It was terrifying because this amazing, sweet, wonderful human being came this close to not being around anymore — this person we loved so much after just one year. Obviously you need to make the show, but the important thing was making sure she was in a safe situation. You ask yourself: Is she as safe doing this show as if she was not doing it? If she was home sitting on her couch? She was so gung ho; the main thing for us was making sure she wouldn’t put herself [in dangerous situations]. She would say, “Yeah, I just had brain surgery, and if I need to gallop on a horse down a mountainside, I’ll do it.” You would have to tell her no, because she would never say no.

EMILIA CLARKE: In all of my years on the show, I never put self-health first, which is probably why everyone else was worrying, as they could see that. They didn’t want to work me too hard. I was like, “Don’t think I’m a failure; don’t think I can’t do the job that I’ve been hired to do. Please don’t think I’m going to fuck up at any moment.” I had the Willy Wonka golden ticket. I wasn’t about to hand that in. [Source]