Flask: serve template in another folder (other than 'templates/' directory)

I have generated sphinx documentation for my project into documentation folder. Now I want to serve that using a flask server.

This is my project structure. I want to serve example.html from the documentation folder. That folder also has relevant CSS files required for it.

app/
    module1/
    module2/
    documentation/
        build/
            example.html
            styles.css
            ...
    templates/
        other_files.html
        ...

app_controller.py

@application.route("/doc", methods=["GET"])
@log_exceptions_to_github
def doc():
    return render_template('/build/index.html')

Issue:

Flask looks for HTML files in the "templates" folder only by default.

So I am not able to serve this. Note that copying from documentation dir to templates dir is not what I want to do because of project requirements.

I want to add "documentation" folder as a templates directory along with the default one.

I have tried this but it is not working: https://stackoverflow.com/a/13598839/2286762