Stephen Hawking has revealed that at in 1985 he was so ill that doctors offered to switch off his life support.
At the time the professor was writing A Brief History Of Time, a book which went on to sell millions and propel his to international fame.
According to The Sunday Times, a new film shows Professor Hawking telling of how he thought contracting pneumonia would stop him from completing the book.
But his first wife, Jane Hawking, refused to switch off the machine and demanded doctors in Switzerland return him to Cambridge. The life-saving treatment left him unable to speak.
In the film, Hawking, whose motor neurone disease keeps him in a wheelchair, says: "The doctors thought I was so far gone that they offered Jane (the option) to turn off the machine.
"The weeks of intensive care that followed were the darkest of my life.
"But slowly the drugs worked, though a small incision in my throat robbed me of my ability to talk.
"I was then put on a ventilator and hopes of finishing my book seemed over."
Hawking speaks openly about his two failed marriages, his second to nurse Elaine Mason, and his constantly precarious health in the documentary which coincides with the release of his biography.
The film is due for release on September 20.