add parent template class to child WP

function cc_body_class( $classes ) {
    global $post;
    if ( is_page() ) {
        // Has parent / is sub-page
        if ( $post->post_parent ) {
            # Parent post name/slug
           $parent = get_post( $post->post_parent );
            $classes[] = 'parent-slug-'.$parent->post_name;
            // Parent template name
            $parent_template = get_post_meta( $parent->ID, '_wp_page_template', true);
            if ( !empty($parent_template) )
                $classes[] = 'parent-template-'.sanitize_html_class( str_replace( '.', '-', $parent_template ), '' );
        }
    }
    return $classes;
}
add_filter( 'body_class', 'cc_body_class' );