Get a term's parent TID

Provided we have the TID of the child term, the parent is found by:

<?php
$parent = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadParents($child_term_id);
reset($parent);
$parent_id = $parent->id();

Or to yield for instance the parent term's name: 

$parent_name = $parent->getName();