{% if article.related_posts %}
{% from '_includes/_defaults.html' import RELATED_POSTS_LABEL with context %}
<section>
    <h2>{{ RELATED_POSTS_LABEL }}</h2>
<ul class="related-posts-list">
{% for related_post in article.related_posts %}
    {% set title = related_post.title|striptags %}
    {% set htitle = title %}
    {%if related_post.subtitle %}
        {% set htitle = title + ' - ' + related_post.subtitle %}
        {% set title = title + ' ' +  '<small>' + related_post.subtitle + '</small>' %}
    {% endif %}
<li><a href="{{ SITEURL }}/{{ related_post.url }}" title="{{ htitle }}">{{ title }}</a></li>
{% endfor %}
</ul>
<hr />
</section>
{% endif %}


{% if article.related_posts %}
{% from '_includes/_defaults.html' import RELATED_POSTS_LABEL with context %}
<section>
    <h2>{{ RELATED_POSTS_LABEL }}</h2>
<ul class="related-posts-list">
{% for related_post in article.related_posts|sort(attribute = 'date') %}
    {% set title = related_post.title|striptags %}
    {% set htitle = title %}
    {%if related_post.subtitle %}
        {% set htitle = title + ' - ' + related_post.subtitle %}
        {% set title = title + ' ' +  '<small>' + related_post.subtitle + '</small>' %}
    {% endif %}
<li><a href="{{ SITEURL }}/{{ related_post.url }}" title="{{ htitle }}">{{ title }}</a></li>
{% endfor %}
</ul>
<hr />
</section>
{% endif %}


Sort articles in the related posts section by date in ascending order
Sort articles in the related posts section by date in ascending order

I think ascending is better. This way older article will appear on top
of the list. Recent related articles may already appear in recent posts
section. You need to bubble up older articles.
