diff --git a/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php b/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php
index 5f144a4df3..b2259cd39f 100644
--- a/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php
@@ -184,7 +184,7 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
         $source_id_values[$migration_id] = $value;
       }
       // Break out of the loop as soon as a destination ID is found.
-      if ($destination_ids = $migration->getIdMap()->lookupDestinationId($source_id_values[$migration_id])) {
+      if ($destination_ids = $migration->getIdMap()->lookupDestinationIds($source_id_values[$migration_id])) {
         break;
       }
     }
@@ -235,7 +235,12 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
       }
     }
     if ($destination_ids) {
-      if (count($destination_ids) == 1) {
+      if (count($destination_ids[0]) == 1) {
+        $destination_ids = array_map(function ($a) {
+          return reset($a);
+        }, $destination_ids);
+      }
+      if (count($destination_ids) == 1 && !is_array($destination_ids[0])) {
         return reset($destination_ids);
       }
       else {
diff --git a/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php.orig b/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php.orig
new file mode 100644
index 0000000000..5f144a4df3
--- /dev/null
+++ b/core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php.orig
@@ -0,0 +1,280 @@
+<?php
+
+namespace Drupal\migrate\Plugin\migrate\process;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\MigrateSkipProcessException;
+use Drupal\migrate\Plugin\MigratePluginManagerInterface;
+use Drupal\migrate\Plugin\MigrationPluginManagerInterface;
+use Drupal\migrate\Plugin\MigrateIdMapInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Looks up the value of a property based on a previous migration.
+ *
+ * It is important to maintain relationships among content coming from the
+ * source site. For example, on the source site, a given user account may
+ * have an ID of 123, but the Drupal user account created from it may have
+ * a uid of 456. The migration process maintains the relationships between
+ * source and destination identifiers in map tables, and this information
+ * is leveraged by the migration_lookup process plugin.
+ *
+ * Available configuration keys
+ * - migration: A single migration ID, or an array of migration IDs.
+ * - source_ids: (optional) An array keyed by migration IDs with values that are
+ *   a list of source properties.
+ * - stub_id: (optional) Identifies the migration which will be used to create
+ *   any stub entities.
+ * - no_stub: (optional) Prevents the creation of a stub entity when no
+ *   relationship is found in the migration map.
+ *
+ * Examples:
+ *
+ * Consider a node migration, where you want to maintain authorship. If you have
+ * migrated the user accounts in a migration named "users", you would specify
+ * the following:
+ *
+ * @code
+ * process:
+ *   uid:
+ *     plugin: migration_lookup
+ *     migration: users
+ *     source: author
+ * @endcode
+ *
+ * This takes the value of the author property in the source data, and looks it
+ * up in the map table associated with the users migration, returning the
+ * resulting user ID and assigning it to the destination uid property.
+ *
+ * The value of 'migration' can be a list of migration IDs. When using multiple
+ * migrations it is possible each use different source identifiers. In this
+ * case one can use source_ids which is an array keyed by the migration IDs
+ * and the value is a list of source properties.
+ *
+ * @code
+ * process:
+ *   uid:
+ *     plugin: migration_lookup
+ *       migration:
+ *         - users
+ *         - members
+ *       source_ids:
+ *         users:
+ *           - author
+ *         members:
+ *           - id
+ * @endcode
+ *
+ * If the migration_lookup plugin does not find the source ID in the migration
+ * map it will create a stub entity for the relationship to use. This stub is
+ * generated by the migration provided. In the case of multiple migrations the
+ * first value of the migration list will be used, but you can select the
+ * migration you wish to use by using the stub_id configuration key:
+ *
+ * @code
+ * process:
+ *   uid:
+ *     plugin: migration_lookup
+ *     migration:
+ *       - users
+ *       - members
+ *     stub_id: members
+ * @endcode
+ *
+ * In the above example, the value of stub_id selects the members migration to
+ * create any stub entities.
+ *
+ * To prevent the creation of a stub entity when no relationship is found in the
+ * migration map, use no_stub:
+ *
+ * @code
+ * process:
+ *   uid:
+ *     plugin: migration_lookup
+ *     migration: users
+ *     no_stub: true
+ *     source: author
+ * @endcode
+ *
+ * @see \Drupal\migrate\Plugin\MigrateProcessInterface
+ *
+ * @MigrateProcessPlugin(
+ *   id = "migration_lookup"
+ * )
+ */
+class MigrationLookup extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The process plugin manager.
+   *
+   * @var \Drupal\migrate\Plugin\MigratePluginManager
+   */
+  protected $processPluginManager;
+
+  /**
+   * The migration plugin manager.
+   *
+   * @var \Drupal\migrate\Plugin\MigrationPluginManagerInterface
+   */
+  protected $migrationPluginManager;
+
+  /**
+   * The migration to be executed.
+   *
+   * @var \Drupal\migrate\Plugin\MigrationInterface
+   */
+  protected $migration;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration, MigrationPluginManagerInterface $migration_plugin_manager, MigratePluginManagerInterface $process_plugin_manager) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->migrationPluginManager = $migration_plugin_manager;
+    $this->migration = $migration;
+    $this->processPluginManager = $process_plugin_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $migration,
+      $container->get('plugin.manager.migration'),
+      $container->get('plugin.manager.migrate.process')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    $migration_ids = $this->configuration['migration'];
+    if (!is_array($migration_ids)) {
+      $migration_ids = [$migration_ids];
+    }
+    if (!is_array($value)) {
+      $value = [$value];
+    }
+    $this->skipOnEmpty($value);
+    $self = FALSE;
+    /** @var \Drupal\migrate\Plugin\MigrationInterface[] $migrations */
+    $destination_ids = NULL;
+    $source_id_values = [];
+    $migrations = $this->migrationPluginManager->createInstances($migration_ids);
+    foreach ($migrations as $migration_id => $migration) {
+      if ($migration_id == $this->migration->id()) {
+        $self = TRUE;
+      }
+      if (isset($this->configuration['source_ids'][$migration_id])) {
+        $configuration = ['source' => $this->configuration['source_ids'][$migration_id]];
+        $source_id_values[$migration_id] = $this->processPluginManager
+          ->createInstance('get', $configuration, $this->migration)
+          ->transform(NULL, $migrate_executable, $row, $destination_property);
+      }
+      else {
+        $source_id_values[$migration_id] = $value;
+      }
+      // Break out of the loop as soon as a destination ID is found.
+      if ($destination_ids = $migration->getIdMap()->lookupDestinationId($source_id_values[$migration_id])) {
+        break;
+      }
+    }
+
+    if (!$destination_ids && !empty($this->configuration['no_stub'])) {
+      return NULL;
+    }
+
+    if (!$destination_ids && ($self || isset($this->configuration['stub_id']) || count($migrations) == 1)) {
+      // If the lookup didn't succeed, figure out which migration will do the
+      // stubbing.
+      if ($self) {
+        $migration = $this->migration;
+      }
+      elseif (isset($this->configuration['stub_id'])) {
+        $migration = $migrations[$this->configuration['stub_id']];
+      }
+      else {
+        $migration = reset($migrations);
+      }
+      $destination_plugin = $migration->getDestinationPlugin(TRUE);
+      // Only keep the process necessary to produce the destination ID.
+      $process = $migration->getProcess();
+
+      // We already have the source ID values but need to key them for the Row
+      // constructor.
+      $source_ids = $migration->getSourcePlugin()->getIds();
+      $values = [];
+      foreach (array_keys($source_ids) as $index => $source_id) {
+        $values[$source_id] = $source_id_values[$migration->id()][$index];
+      }
+
+      $stub_row = $this->createStubRow($values + $migration->getSourceConfiguration(), $source_ids);
+
+      // Do a normal migration with the stub row.
+      $migrate_executable->processRow($stub_row, $process);
+      $destination_ids = [];
+      $id_map = $migration->getIdMap();
+      try {
+        $destination_ids = $destination_plugin->import($stub_row);
+      }
+      catch (\Exception $e) {
+        $id_map->saveMessage($stub_row->getSourceIdValues(), $e->getMessage());
+      }
+
+      if ($destination_ids) {
+        $id_map->saveIdMapping($stub_row, $destination_ids, MigrateIdMapInterface::STATUS_NEEDS_UPDATE);
+      }
+    }
+    if ($destination_ids) {
+      if (count($destination_ids) == 1) {
+        return reset($destination_ids);
+      }
+      else {
+        return $destination_ids;
+      }
+    }
+  }
+
+  /**
+   * Skips the migration process entirely if the value is FALSE.
+   *
+   * @param mixed $value
+   *   The incoming value to transform.
+   *
+   * @throws \Drupal\migrate\MigrateSkipProcessException
+   */
+  protected function skipOnEmpty(array $value) {
+    if (!array_filter($value)) {
+      throw new MigrateSkipProcessException();
+    }
+  }
+
+  /**
+   * Create a stub row source for later import as stub data.
+   *
+   * This simple wrapper of the Row constructor allows sub-classing plugins to
+   * have more control over the row.
+   *
+   * @param array $values
+   *   An array of values to add as properties on the object.
+   * @param array $source_ids
+   *   An array containing the IDs of the source using the keys as the field
+   *   names.
+   *
+   * @return \Drupal\migrate\Row
+   *   The stub row.
+   */
+  protected function createStubRow(array $values, array $source_ids) {
+    return new Row($values, $source_ids, TRUE);
+  }
+
+}
diff --git a/core/modules/migrate/tests/src/Unit/process/MigrationLookupTest.php b/core/modules/migrate/tests/src/Unit/process/MigrationLookupTest.php
index dd18928d4a..fcd8e5f3e5 100644
--- a/core/modules/migrate/tests/src/Unit/process/MigrationLookupTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/MigrationLookupTest.php
@@ -30,7 +30,7 @@ public function testTransformWithStubSkipping() {
     $destination_id_map = $this->prophesize(MigrateIdMapInterface::class);
     $destination_migration = $this->prophesize(MigrationInterface::class);
     $destination_migration->getIdMap()->willReturn($destination_id_map->reveal());
-    $destination_id_map->lookupDestinationId([1])->willReturn(NULL);
+    $destination_id_map->lookupDestinationIds([1])->willReturn(NULL);
 
     // Ensure the migration plugin manager returns our migration.
     $migration_plugin_manager->createInstances(Argument::exact(['destination_migration']))
@@ -62,7 +62,7 @@ public function testTransformWithStubbing() {
     $destination_migration->getIdMap()->willReturn($destination_id_map->reveal());
     $migration_plugin_manager->createInstances(['destination_migration'])
       ->willReturn(['destination_migration' => $destination_migration->reveal()]);
-    $destination_id_map->lookupDestinationId([1])->willReturn(NULL);
+    $destination_id_map->lookupDestinationIds([1])->willReturn(NULL);
     $destination_id_map->saveIdMapping(Argument::any(), Argument::any(), MigrateIdMapInterface::STATUS_NEEDS_UPDATE)->willReturn(NULL);
 
     $configuration = [
@@ -130,7 +130,7 @@ public function testSuccessfulLookup($source_id_values, $destination_id_values,
     $migration_plugin->id()->willReturn(uniqid());
 
     $id_map = $this->prophesize(MigrateIdMapInterface::class);
-    $id_map->lookupDestinationId($source_id_values)->willReturn($destination_id_values);
+    $id_map->lookupDestinationIds($source_id_values)->willReturn([$destination_id_values]);
     $migration_plugin->getIdMap()->willReturn($id_map->reveal());
 
     $migration_plugin_manager->createInstances(['foobaz'])
diff --git a/core/modules/migrate/tests/src/Unit/process/MigrationTest.php b/core/modules/migrate/tests/src/Unit/process/MigrationTest.php
index cade905a4d..06d02bca8b 100644
--- a/core/modules/migrate/tests/src/Unit/process/MigrationTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/MigrationTest.php
@@ -108,7 +108,7 @@ public function testTransformWithStubbing() {
    */
   protected function getMigration() {
     $id_map = $this->prophesize(MigrateIdMapInterface::class);
-    $id_map->lookupDestinationId([1])->willReturn(NULL);
+    $id_map->lookupDestinationIds([1])->willReturn(NULL);
     $id_map->saveIdMapping(Argument::any(), Argument::any(), MigrateIdMapInterface::STATUS_NEEDS_UPDATE)->willReturn(NULL);
 
     $migration = $this->prophesize(MigrationInterface::class);
@@ -150,7 +150,7 @@ public function testSuccessfulLookup($source_id_values, $destination_id_values,
     $this->migration_plugin->id()->willReturn(uniqid());
 
     $id_map = $this->prophesize(MigrateIdMapInterface::class);
-    $id_map->lookupDestinationId($source_id_values)->willReturn($destination_id_values);
+    $id_map->lookupDestinationIds($source_id_values)->willReturn([$destination_id_values]);
     $this->migration_plugin->getIdMap()->willReturn($id_map->reveal());
 
     $this->migration_plugin_manager->createInstances(['foobaz'])