function wpc_extra_get_post_related_posts() {
    $post_id = get_the_ID();
    $terms = get_the_terms($post->ID, array('category', 'post_tag'));

    $term_ids = array();
    if ( is_array( $terms ) ) {
        foreach ( $terms as $term ) {
            $term_ids[] = $term->term_id;
        }
    }

    $related_posts = new WP_Query( array(
        'tax_query'      => array(
            array(
                'taxonomy' => 'category',
                'field'    => 'id',
                'terms'    => $term_ids,
                'operator' => 'IN',
            ),
        ),
        'post_type'      => 'post',
        'posts_per_page' => '4',
        'orderby'        => 'rand',
        'post__not_in'   => array( $post_id ),
    ) );

    if ( $related_posts->have_posts() ) {
        return $related_posts;
    } else {
        return false;
    }
}