iOS Singleton class inside MVC architecture

Most of the iOS apps are based on MVC Design pattern, and we are using Singleton classes inside our apps from many years. I know that Singleton itself is a design pattern and many consider it as anti-pattern and all that good bad stuff about singletons.

But if you consider MVC as a overall architecture to your app development I would like to understand where does a singleton be categorised in it. Is it a Model, or View or Controller? if so why? if it does not belong to any of these three then what it is?

This might seem a silly question but it keeps bothering me as I was asked this question in an interview in a reputed company.