sort alphabetically by last name if post title is a name

surname-sort.php

<?php 
  $args = array(
    'post_type'         => 'post',
    'posts_per_page'    => -1,
  );
  
  $the_posts = get_posts($args);
                        
  foreach($the_posts as $single_post){
    $single_id = $single_post->ID;
    $single_name = $single_post->post_title;
    //detect last empty space & characters following that
    $single_name = substr($single_name, strrpos($single_name, ' ') + 1);
    //build a new array w/ ID as $key & Surname as $value
    $abc_name_array[$single_id] = $single_name;
  }
  
  //sort that array alphabetically!
  asort($abc_name_array);

  //now loop through it all, remember $key = ID & $value = Surname
  foreach($abc_name_array as $key => $value){
  ?>
    <div id="post-<?php $key; ?>" <?php post_class('post'); ?>>
      <h2 class="post-title">
        <a href="<?php echo get_permalink($key); ?>" title="<?php echo get_the_title($key); ?>">
          <?php echo get_the_title($key); ?>
        </a>
      </h2>
    </div><!-- .post -->
  <?php } ?>