Very sad to hear. I liked Rush over the years, though I wasn't a fanatic about it. However, I would just marvel at the drum playing in their songs when I would listen, and I'm not even a musician.
Not surprised that few people knew he was fighting cancer. He was always an extremely private person.
I saw the band's bio "Beyond the Lighted Stage," and I think I've posted on here before my favorite story from that film. They said that before joining Rush, Peart was content to leave his music dreams behind and start working with his Dad at a farm-equipment parts dealership. When he had the chance to join Rush, his dad sat him down and told him he needed to see his musical aspirations through and that he should take this opportunity, and the rest is history. So, RIP Neil and a salute to Glen Peart for letting us enjoy his son's talent.