include featured image in popup

I have the following code in my single.php file to load the featured image into the content. The image however doesn’t load into the lightbox. How can I get the featured image to load in the lightbox?

<?php if ($featuredincontent && has_post_thumbnail()) {
$large_image_url = wp_get_attachment_image_src( get_post_thumbnail_id(), 'full');
echo '<a href="' . $large_image_url[0] . '" >';
the_post_thumbnail('medium', array( 'class' => 'alignright'));
echo '</a>';
}
?>

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