Remove the PHP snippet that Fernando provided, and add this instead:
function display_modified_author(){
$author = get_the_author();
$mod_author = get_the_modified_author();
if ( $mod_author !== $author ){
return 'Fact Checked by: ' . $mod_author;
}
}
add_shortcode('mod_author','display_modified_author');
Then where you want to display the modified author, add a Headline block, and inside that add the [mod_author] shortcode.
It will only display if the post has a modified_author