Another couple articles. One says he didn't know how serious his cancer was, another says it was pancreatic.  One of the deadliest out there. Michael Landon died of the same.

I've not read this first one in detail as it's long.

http://www.telegraph.co.uk/news/celebritynews/12099543/Alan-rickman-dead-at-69-latest.html

http://www.independent.co.uk/news/people/alan-rickman-british-actor-died-from-pancreatic-cancer-a6814686.html