Arthur Koestler was born on September 5, 1905 and died on March 3, 1983. Arthur Koestler would have been 77 years old at the time of death or 106 years old today.
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Though we know the estimated date of death (537 at the Battle of Camlann), we don't know when he was born. Of course this is all assuming he ever actually existed. -~Iolaos~-