Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: cannot be cast to class

Question

Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: 
  class application.Admin_HomePage_Controller cannot be cast to 
  class application.HomePage_Controller
  (application.Admin_HomePage_Controller and 
  application.HomePage_Controller are in unnamed module of loader 'app')
  at DB.DBUtils.changeScene

I wanted different changeScene(s) for 2 types of users- general users & admin user (based on login form username).

Here is the main code of try-block inside changeScene :

if(username != null) {     // if user entered username in login form
    try {
    FXMLLoader loader = new FXMLLoader(DBUtils.class.getResource(fxmlfile));
    root = loader.load();
            
    if(username == "admin") {
        Admin_HomePage_Controller adminhomepagecontroller = loader.getController();
        adminhomepagecontroller.setUserInfo(username);
}
else {
    HomePage_Controller homepagecontroller = loader.getController();
    homepagecontroller.setUserInfo(username);
}
} catch(IOException e) {
    e.printStackTrace();
}
}