Terry Jones has bowel cancer. His doctors believe they've caught it early, though, so things may not be as bad as they could.
This is the second Python so far with cancer; Graham Chapman died in 1989 from throat cancer.
Jones has always, to me, been the Python who quietly drove the troupe with his ideas, despite never catapulting to stardom as John Cleese and Michael Palin have. His commentaries on the Python experience (and outside of the Pythons) are always insightful.
Best wishes and a speedy recovery to Terry.