The author of The Fault In Our Stars, the novel about two teenagers dying of cancer, has spoken of how his faith was challenged by his experience of working as a student chaplain at a children's hospital as an aspiring minister.

He told the Huffington Post that after six months there he realised that he "wasn't cut out" for ministry.

He said to host Nancy Redd: "It was a lot harder than it had been in my imagination. I realised that ... all of these fancy theological ideas that I had from reading lots of theology books didn't really matter much when it came time to be with kids who were dying, or when it came time to be with families who had just lost their children. All of that complicated theology sort of fell by the wayside for me."

He continued: "Lots of people, they don't experience what I experienced, but my experience was that it fell apart and all there was was loss and pain."

Writing the book, Green said, was "a way of "trying to understand some of the ways through that [experience]". "I am amazed by the people who do it every day," he said. "They have not just courage but tremendous guts."

The Fault In Our Stars is about the romance between two teenagers with cancer, Augustus Waters and Hazel Grace Lancaster, who meet at a support group after Hazel's mother sends her there to help overcome her depression. The film of the book, starring Shailene Woodley and Ansel Elgort, was released last year to public and critical acclaim and made more than $306 million worldwide, having been made on a $12 million budget.