text: The two-page note, addressed to Mrs Ellis and dated 19 August 1945, finds him dealing with the subject of joy.
  It was found by its owner in a copy of Lewis's book, A Problem of Pain, bought years before.
  Auctioneer Chris Albury said "keen interest worldwide" had boosted the guide price from £1,500.
  Dominic Winter Auctioneers in South Cerney said the letter had been bought by a private buyer from California.
  "It's a wonderful, thoughtful letter by one of the most highly regarded English writers of the 20th Century," Mr Albury said.
  "Any original and unpublished letter that gives new insights into a collectable writer's ideas is going to have an appeal, and this one has literary, autobiographical, philosophical and theological content, so ticks every box.
  "The letter was written just days after Japan's surrender at the end of the Second World War and perhaps the idea of joy, which he thought very unlike pleasure, was once again on his mind."
  In the letter, which is in "very good" condition, Lewis writes: "Real joy...  jumps under one's ribs and tickles down one's back and makes one forget meals and keeps one (delightedly) sleepless o' nights.
  "It shocks one awake when the other (security and prosperity) puts one to sleep.
  "My private table is one second of joy is worth 12 hours of pleasure."
  Mr Albury said the subject of joy was a "continual theme" throughout Lewis's life.
  "Interesting, too, is the fact that he was to meet and marry a woman called Joy a few years later," he said.
target: An unpublished letter from writer and scholar CS Lewis has made £4,600 at auction in Gloucestershire, more than three times the original estimate.