Novel author Yamaguchi Noboru posted in his twitter that he will be hospitalized tomorrow and will take a major surgery in August. He said he would have been dead if he had missed the chance to take the operation. "The 21st volume of Zero no Tsukaima novel will be delayed at least for two months. Please forgive me! Damn! I'll live on. I had been desperate, but I miraculously got an opportunity to take the operation. There is a possibility of survival. I really want to live."

Source: Yamaguchi's twitter

Update July 15th
According to Media Factory, Yamaguchi is suffering from a terminal-stage cancer. A tumor was found this February. At that point, it was impossible to carry out a surgery but a shrinkage of the tumor was observed in May thanks to the effect of anti-cancer drugs. He said he has already completed the outlines of the remaining two volumes of Zero no Tsukaima novel and wanted to publish them as soon as possible.

Source: Media Factory

Update August 4th
Yamaguchi posted in his twitter that the operation was finished and he was allowed to walk outside.