Returning a value in constructor function of a class

So far I have a PHP class with the constructor

public function __construct ($identifier = NULL)
{
 // Return me.
if ( $identifier != NULL )
{
  $this->emailAddress = $identifier;
  if ($this->loadUser() )
    return $this;      
  else
  {
// registered user requested , but not found ! 
return false;
  }
}

the functionality of loadUser is to look up the database for a particular email address. When i set the identifier to some email that i'm sure it's not in the database; the first IF is get passed, and goes to the first ELSE. here the constructor should return FALSE; but instead, it returns an object of the class with all NULL values !

how do i prevent this? thanks

EDIT:

thank you all for the answers. that was quite fast ! I see that the OOP way is to throw an Exception. So a throw one, my question changes that what should i do with the exception?? php.net's manual is pretty confusing !

    // Setup the user ( we assume he is a user first. referees, admins are   considered users too )
    try { $him = new user ($_emailAddress);
    } catch (Exception $e_u) { 
      // try the groups database
      try { $him = new group ($_emailAddress); 
      } catch (Exception $e_g) {
          // email address was not in any of them !!  
        }
    }