How to show 404 whenever/wherever I want

Hello. In my site I have some pages that I only want a logged in administrator to see. If the admin is not logged in I don't want to show the typical login page or some error, I want to show error 404. In CodeIgniter 3 we could type show_404() wherever we wanted in the controller - and as soon as the code got to it - bam! 404. How can I do this in CI 4?

You can see things I made with codeigniter here: itart.pro its not overly impressive as I have very little time to learn.