He may be one of the world's most eminent scientists, but one thing remains a mystery to Professor Stephen Hawking - women.
When asked what he thinks most about during the day the physicist, who turns 70 on Sunday, said: "Women. They are a complete mystery."
Prof Hawking was diagnosed with amyotrophic lateral sclerosis (ALS), a form of motor neurone disease, when he was 22 and was not expected to live for more than a few years.
But he went on to become one of the world's most renowned physicists, publishing three best-selling books, including the well-known A Brief History Of Time, and has been awarded a number of honorary degrees, medals, and a CBE in 1982. He has also been married twice and has three children.
Prof Hawking made his comment about women in an interview with New Scientist ahead of his birthday on Sunday. He also told the magazine his "biggest blunder" was thinking that information was destroyed in black holes.
"This was my biggest blunder, or at least my biggest blunder in science," he said.
He was also asked what he would study if he were a young physicist starting out today, to which he replied: "I would have a new idea that would open up a new field."
The interview comes a week after Prof Hawking's technician Sam Blackburn, responsible for the past five years for the technology that allows him to communicate, told New Scientist the physicist's facial muscles that control his voice synthesiser are fading and new technology will be needed.
"Stephen's rate of speech is down to about one word per minute, and while I am making slight advances in the technology he is using, the nerve decay has now reached the point where we need to move to some new technology."
Prof Hawking will mark his 70th birthday with a speech at a public symposium at the University of Cambridge on Sunday.