Not really, not without the cooperation of your controller.  You can  
subscribe to the event if the TextBox control is public, and depending on  
what you are really trying to do, you _might_ be able to cancel or  
otherwise undo something that the controller does in response to the event.

For example, assuming your client class subscribes to the event after the  
controller, and assuming all you want to do is handle something in the  
event that the controller doesn't, or prevent the controller from  
signaling that it has handled the event, then you could just set the  
Handled property in the event and since your code would execute after the  
controller's, you win.

But you can't stop the controller from handling the event altogether.  And  
even in the example I describe, it's a somewhat fragile situation, as  
you're completely dependent on the assumption that the controller  
subscribes to the event before you do.

If you want to override the controller's own event handling, you should  
change the controller so that it's designed to allow this.  That would not  
be hard at all and the resulting code would be a lot more robust and  
maintainable.

Pete