Rubenstern is a land or town near Daventry.
It is mostly known for the Rubenstern fiasco. Where Chester and possibly others apparently ate too much on Ice Cream for Breakfast Day, or ate chunderblossom flavoured ice cream. Which caused distress, and in need of assistance. Presumably no one came to the rescue before problems escalated, and Chester Hobblepot became sick with a severe stomach ache. It took Daventry's Knights to come to the rescue.
Behind the scenesEdit
The full context is not clear, and its possible Rubenstern could be a person. But at least based on the information in chapter 2 it seems it refers to something that happened to Chester Hobblepot and may have involved chunderblossoms. This may suggest its actually a location name.