John Green, the author of best-selling novel The Fault in Our Stars, remembers receiving a long, full-of-praise email from an excited young Hollywood actress named Shailene Woodley.
"I didn't really understand who she was," Green recently confessed to AAP.
Woodley's breakthrough role was in the Alexander Payne-directed, George Clooney-starring 2011 comedy-drama The Descendants, but despite the critical applause and a Golden Globe nomination the Los Angeles-raised actress enjoyed, Green didn't notice.
Woodley was a fan of The Fault in Our Stars, a love story inspired by Green's stint as a student chaplain in a children's hospital.
Indianapolis-born Green, 36, was inspired by the children, particularly Esther Earl, a 16-year-old who succumbed to metastasised papillary thyroid cancer in 2010.
Esther and the other children were inflicted by terminal cancer, but were full of life.
"I did write a letter to John Green to basically say, 'Thank you, and I'm so grateful you were able to write this gift to share with the world'," Woodley, 22, who also starred in this year's sci-fi hit Divergent, said.
"I wanted to make sure this movie was made because my life was transformed by reading the book and the script.
"I could only imagine how many lives it would transform if it was to be a film."
The main character in The Fault in Our Stars, 16-year-old Hazel Grace Lancaster, has thyroid cancer that has spread to her lungs and to breathe she is forced to lug a portable oxygen tank around.
Hazel and another teen cancer patient, Augustus Waters, bond over their love of books, particularly a novel by reclusive author Peter Van Houten.
Just as Woodley sent an email to Green, in the novel Hazel reaches out to Van Houten with a heartfelt message.
Hollywood first began pursuing Green for the rights to turn The Fault in Our Stars into a movie before the novel was published.
He rejected the offers because he wanted to protect the story.
Then the producing team behind the Twilight adaptation, Wyck Godfrey and Marty Bowen, built a trusting relationship with Green, promising to remain faithful to the book's themes and characters.
Green closely monitored the casting.
When he received that email from Woodley, he sent a reply.
"I responded like, 'That's very flattering but I'm not a casting director"," Green said.
"It was a very brief response."
Then Green, going through the audition tapes for Hazel, came across Woodley's.
Woodley performed in her audition a pivotal scene in the book and film where Hazel offers the line, "Some infinities are bigger than other infinities".
"Oh, it just gutted me," Green, named by Time magazine as one of the 100 most influential people in the world because of the way his books connect with teenagers and young adults, said.
"I was blown away.
"I was in tears and just so grateful that she had even auditioned for it.
"I immediately called the producer and said, 'What do I have to do? Can I call her? Can I go to LA?'
"They were like, 'She wants to do the movie. It is going to be fine'.
"I knew then she was going to be the perfect Hazel".
The Fault in Our Stars opens in Australia on June 5.