In the new issue of Entertainment Weekly, author John Green reveals that he was just as surprised as anyone by the runaway success of his teens-with-cancer romance The Fault In Our Stars, which has been translated into 46 languages and has been on the New York Times best-seller list for 116 consecutive weeks.

“I tried to write the funniest, most honest love story I could about these kids who were living with a difficult disease. I never thought it would be popular,” Green says. “I certainly never imagined it would be a movie.”

The movie’s producers, it seems, never imagined that it would be a movie either. According to Fox 2000 president Elizabeth Gabler, the prospect of making a love story about teens with cancer was just too risky. The studio was already in the middle of Life of Pi, a $100 million movie set almost entirely on a lifeboat, and didn’t want to have another high-risk venture on her plate.

But due to the persistence of producer Wyck Godfrey, Gabler eventually changed her mind. “Wyck called me and said, ‘You can’t pass on this. You have to do this,” she says. “I said, ‘Why are you doing this to me?’ And he said, ‘Because. It makes you remember when you were a teenager and you were in love for the first time and you didn’t want to hang up the phone.'”

After getting the greenlight, the movie faced its biggest obstacle yet: finding actors who could play Hazel and Gus, the cancer-stricken teen heroes of Green’s novel.

Despite having written a 13,000 word letter explaining why she should be Hazel, director John Boone was reluctant to cast Shailene Woodley, who he considered to be too old for the part. (Hazel is 16 in the book, Woodley is 22 in real life). But two minutes into Woodley’s audition, Boone changed his mind. “I was on the floor,”; says Boone. “I thought, “Why am I fighting this? There’s nobody better than her. She’s awesome.'”;

When Green watched Woodley’s audition on videotape, he had a similar response. “I suddenly was in a blind panic, jumping on the phone and screaming, “We must lock this down! It has to be Shailene Woodley! She is Hazel!”;

The new issue of EW hits newsstands May 2.