Really depends on how your domain forwarding is set up.
Some domain forwarders will send all traffic to a single URL. Eg http://devierdemacht.be, http://devierdemacht.be/home.php and http://devierdemacht.be/uncategorized/hello-world/ will all go to a single webpage.
However you can also do domain forwarding that sends to the new URL + everything else in the URL. In the cases about those links would go to http://d-eye.be/devierdemacht/, http://d-eye.be/devierdemacht/home.php and http://d-eye.be/devierdemacht/uncategorized/hello-world/
The latter domain forwarding approach would allow you to have a structure as you wish. If you change the settings in WordPress you'll get the links to be the devierdemacht.be URL.
That said, it's pretty inefficient to do this as you are constantly going between two URLs and you'll also have issues with SEO. So I'd not bother.