Professor Stephen Hawking was not well enough to attend an event to celebrate his 70th birthday at the University of Cambridge.
He was due to look back at his life at the free public symposium at the University's Centre for Theoretical Cosmology, but instead had to make do with watching events unfold on the internet.
All the tickets for the free event were snapped up months ago which is a testament to Prof Hawking's enduring appeal, but the university revealed he would not be attending the event soon after it began.
Cambridge University tweeted: "Prof Hawking not well enough to attend today but is watching the live stream. Happy birthday Prof and get well soon! #Hawking70."
Speakers at the event included the Astronomer Royal Lord Rees, Prof Saul Perlmutter and one of the world's leading theoretical physicists, Prof Kip Thorne.
Entitled The State of the Universe, the symposium is celebrating how Prof Hawking went on to become one of the most brilliant theoretical physicists since Einstein.
Given only two years to live when he was diagnosed with a form of motor neurone disease in 1963, Prof Hawking has defied medical expectation.
Lord Rees spoke of his admiration for Prof Hawking before the event, commenting on his great feat of reaching the age of 70 after "tragedy struck" and he was diagnosed with a deadly illness.
He said: "Even mere survival would have been a medical marvel, but of course he hasn't merely survived. He has become arguably the most famous scientist in the world - acclaimed for his brilliant researches, for his best-selling books, and, above all, for his astonishing triumph over adversity."
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Talking about how Prof Hawking has become such a cult figure, Lord Rees said that "the concept of an imprisoned mind roaming the cosmos plainly grabbed people's imagination".
