London ( CNN ) Best-selling British fantasy author Terry Pratchett has died at the age of 66 , his website said Thursday . Pratchett , who wrote more than 70 books , including those in his `` Discworld '' series , had been diagnosed with a rare form of Alzheimer 's disease in 2007 . A statement on the website announced the news of his death at home Thursday with `` immeasurable sadness . '' `` I was deeply saddened to learn that Sir Terry Pratchett has died . The world has lost one of its brightest , sharpest minds , '' said Larry Finlay , managing director at Transworld Publishers . `` In over 70 books , Terry enriched the planet like few before him . As all who read him know , 'Discworld ' was his vehicle to satirize this world : He did so brilliantly , with great skill , enormous humor and constant invention . '' Pratchett continued to write following his diagnosis , completing his last book , a new Discworld novel , in the summer of 2014 . Revealing his illness in 2007 , the author -- who had a strong following among fans of fantasy fiction -- said he had been diagnosed with `` a very rare form of early onset Alzheimer 's , '' which he described as `` an embuggerance . '' He said then , `` Frankly , I would prefer it if people kept things cheerful , because I think there 's time for at least a few more books yet . '' According to Thursday 's statement , he had posterior cortical atrophy , a progressive degenerative condition involving the loss and dysfunction of brain cells , particularly at the back of the brain . The last posts on his verified Twitter account , run by Pratchett with close friend Rob Wilkins , give a poignant farewell -- and have already been retweeted thousands of times . `` AT LAST , SIR TERRY , WE MUST WALK TOGETHER , '' the first tweet in the series reads -- an apparent reference to Death , a recurring and generally sympathetic character in the Discworld books , who always speaks in ALL CAPS . `` Terry took Death 's arm and followed him through the doors and on to the black desert under the endless night . `` The End . '' Jeremy Hughes , chief executive of the Alzheimer 's Society , a charitable organization , said Pratchett -- who spoke out publicly about his condition and called for greater funding for Alzheimer 's research -- had `` fundamentally changed the way dementia is seen and understood . '' `` His vehement determination to reduce the stigma of dementia meant he helped drag it out of the shadows -- kicking and screaming at times , '' he said . `` Shouting from the rooftops about the absurdity of how little funding dementia research receives , and fighting for good quality dementia care , he was and will remain the truest of champions for people with the condition . '' Pratchett was also a patron of the British Humanist Association , which paid tribute Thursday to the humor and dedication with which the author `` turned his suffering into a positive campaign . '' Pratchett , who began writing while a provincial newspaper journalist in the 1960s , became a full time writer in 1987 and received the Order of the British Empire `` for services to literature '' from Prince Charles in 1998 . People we 've lost in 2015 . CNN 's Bharati Naik contributed to this report .
Author Terry Pratchett has died age 66 , his website says . Comment: