How do I get the referring entity of a referenced node in a template file? I am struggling since a couple of days with my problem now and I have no idea what else I can do to come to a stage of enlightenment. 

In Drupal 8 I have a content type called "Release" and a content type "Article" which, among others, contains Reviews of Releases. So in Releases I created an entity reference field called "Review" which references Article content type. 

For index pages I could create views of Articles and there I pretty easy could integrate the fields of the referencing release entity via the Relations section in views administration. There the reverse direction of a relationship is not a problem.

How do I access the fields of the release in a node--article.html.twig template?

Edited due to character limitation in the comments section (I hope this is allowed):
Thank you so much, @JeremyM4an, but there was a little misunderstanding due to my bad explanation of the problem. I should have mentioned that article has a reference to a taxonomy term, called field_post_category. 

So a review is an article with field_post_category == 'Review' and finally a release has an entity reference field, called field_review, referring to article. After reading your answer I tried this:

$category_field = $node-&gt;get('field_post_category');
$category_field = $category_field-&gt;getValue();
if( isset($category_field[0]['target_id']) &amp;&amp; $category_field[0]['target_id'] ){
  $term = taxonomy_term_load($category_field[0]['target_id']);
  if($term &amp;&amp; $term-&gt;get('name')-&gt;value == 'Reviews'){
    $release = \Drupal::entityQuery('node')
    -&gt;condition('type', 'release')
    -&gt;condition('field_review.entity:node.nid', $node-&gt;id())
    -&gt;execute();
    // Load release node and store in variables.
    $variables['release'] = Node::load(array_values($release)[0]);
  }
}


But this does not work.
You can get the "relationships" to your referencing node in a preprocess function, in your theme's mytheme.theme file:

function mytheme_preprocess_node(&amp;$variables) {
  if (!empty($variables['node'])) {
    $node = $variables['node'];
    if ($node-&gt;getType() === 'article') {

      // Get the review by article node id.
      $review = \Drupal::entityQuery('node')
        -&gt;condition('type', 'review')
        -&gt;condition('field_article', $node-&gt;id())
        -&gt;execute();

      // Get release by review node id.
      $release = \Drupal::entityQuery('node')
        -&gt;condition('type', 'release')
        -&gt;condition('field_review', array_pop($review))
        -&gt;execute();

      // Load release node and store in variables.
      $variables['release'] = Node::load(array_values($release)[0]);
    }
  }
}


Then you can access the fields in your template:

{{ release.field_name.value }}