Github pages site with hidden content

I have a personal website that's being hosted using Github Pages and with its source code located in a Github repository named my_nickname.github.io.

What I wanted to achieve was to have certain pages, inside the site, only acessible with a password and that it's code wouldn't show on my Github repository.

Is there any way to submit only this part of the source code to a hidden folder inside the repository (so that no one except me could see it) or even create a separate repository with its content and then link it?