This is actually rather sudden, but apparently Noboru Yamaguchi, the author of Zero no Tsukaima was diagnosed with cancer in February but was only officially announced yesterday.
From what I can make out, he will be having a surgery somewhere in August for the cancer. He didn’t really say what kind of cancer he had (either that or I could not read it) and what the surgery is actually for, but he mentioned that he had completed the planning for Zero no Tsukaima volume 22. Unfortunately, the chances are pretty low for him to finish writing it before the surgery.
You can read the original message here.