Poor king, having to rule over a shoujo manga world must be tough. No wonder he needs a straightlaced person to vent with. The knight was a good stopgag measure, but he seems to have his own issues too.
The thing I didn't quite get was why Sara (correctly) thought Rururia would get involved (can she see the future in addition to read minds?), and why the prince and Maria actually involved her without checking with her first that she actually was on board. It seemed like Maria thought that she would automatically side with her if she saw her fall down the stairs and then pretended to be friends. Maybe Maria was a reincarnator? Wouldn't surprise me with the current setup.