How to add a template part via a shortcode?

Hi,I am trying to add a template part via a shortcode. So far I have managed to add the template part but it appears above the content instead of where I put the shortcode. Any help or points in the right direction would be greatly appreciated.
The code I am using is

function client_shortcode() {
return include TEMPLATEPATH . '/clientbox.php' ;
}
add_shortcode('client', 'client_shortcode');