Pages present but still showing 404

[albertocosta]

I have a file secret.php which is built-in in index.php and I desire to explain a 404 error page while someone tries to access secret.php directly. But

header("Location: this_site_certainly_does_not_exist");

in secure.php is not a answer, since I want the URL the user typed (e.g. example.com/secret.php) to be visible in the browser's URL bar when the error page is shown, instead of redirecting.