Terry Pratchett's Last Tweet Was Heartbreakingly Final

English fantasy author Terry Pratchett died Thursday after an ongoing battle with early onset Alzheimer’s disease. He was 66. The author, who published more than 70 books, wrote a closing set of tweets that referenced his Discworld series. They were heartbreakingly final: AT LAST, SIR TERRY, WE MUST WALK TOGETHER. — Terry Pratchett (@terryandrob) March…