My superior has been working on a project for about 6 months (creating a new robust system to replace an old one we have). Lately, he's having less time to work on it and thus, he handed the task to me to continue his work. The work he had done up to the point where he handed it off to me has not been code-reviewed.
The codebase was quite large, and some corners were cut round; functionalities could be split into multiple classes, coding standards were not all respected, etc. The logic, however, is really good (as expected, he is a lot more experienced than I am).
Anyways, I made my changes, but left some critical parts untouched, since I can break the whole project. We have a code review process where all our changes must be reviewed by our peers. During the pull request, a reviewer commented that critical part and asked why it was written without respecting our standards and why it's so different from the rest.
How do I handle the situation? Should I say that it was my superior (who is also his superior) who wrote it or should I just say that I will change it? I don't want to sound like I'm blaming my superior, but at the same time, I'm not sure how to make the changes correctly.