Display a Wordpress post's related posts.

functions.php

<?php

function get_related_posts() {

    $terms = get_the_terms(get_the_ID(), 'category');

    $sub_cat = '';

    if ( $terms && ! is_wp_error( $terms ) ) : 

        if (count($terms) >= 2) {
            foreach ( $terms as $term ) {
                if ($term->parent != 0) {
                    $sub_cat = $term->slug;
                }
            }
        } else {
            foreach ( $terms as $term ) {
                $sub_cat = $term->slug;
            }
        }
        
        
        $args=array(
        'post_type' => 'post',
        'category' => $sub_cat,
        'post__not_in' => array($post->ID),
        'posts_per_page'=>3,
        'ignore_sticky_posts'=>1
        );

        $my_query = new WP_Query($args);

        if( $my_query->have_posts() ) { ?>

        <div class="row">
        <?php   while ($my_query->have_posts()) : $my_query->the_post(); ?>
        
            <div class="large-4 columns">
                <h5><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></h5>
                <p><?php the_excerpt(); ?></p>
            </div>
        <?php
            endwhile;
        }
        wp_reset_query();
        ?>
        </div>
    <?php endif;
}

?>