alternative to wp_link_pages() that only shows link to last page

Crib a bit of code from wp-includes/query.php and bit from wp-includes/post-template.php, add a little, mix and stir, and…

function url_to_last_page() {
  global $post;
  $content = str_replace("\n<!--nextpage-->\n", '<!--nextpage-->', $post->post_content);
  $content = str_replace("\n<!--nextpage-->", '<!--nextpage-->', $content);
  $content = str_replace("<!--nextpage-->\n", '<!--nextpage-->', $content);
  $pages = explode('<!--nextpage-->', $content);
  $numpages = count($pages);
  $ret = _wp_link_page($numpages);
  $ret .= $numpages;
  $ret .= '</a>';
  return $ret;
}
echo url_to_last_page();

wp_list_pages works on index pages so WordPress had to know how to build the links. I just had to find the relevant bits. That need to be inside a Loop, as it depends on the global $post variable. It could be edited to accept a parameter to make it more flexible.