diff --git a/netbox/dcim/models/device_components.py b/netbox/dcim/models/device_components.py
index 9c44e0494..dc8c1e455 100644
--- a/netbox/dcim/models/device_components.py
+++ b/netbox/dcim/models/device_components.py
@@ -1222,6 +1222,8 @@ class ModuleBay(ModularComponentModel, TrackingModelMixin, MPTTModel):
     def save(self, *args, **kwargs):
         if self.module:
             self.parent = self.module.module_bay
+        else:
+            self.parent = None
         super().save(*args, **kwargs)
 
 
diff --git a/netbox/dcim/tests/test_models.py b/netbox/dcim/tests/test_models.py
index e67f32e60..f41509808 100644
--- a/netbox/dcim/tests/test_models.py
+++ b/netbox/dcim/tests/test_models.py
@@ -841,6 +841,32 @@ class ModuleBayTestCase(TestCase):
         nested_bay = module.modulebays.get(name='SFP A-21')
         self.assertEqual(nested_bay.label, 'A-21')
 
+    @tag('regression')  # #20912
+    def test_module_bay_parent_cleared_when_module_removed(self):
+        """Test that the parent field is properly cleared when a module bay's module assignment is removed"""
+        device = Device.objects.first()
+        manufacturer = Manufacturer.objects.first()
+        module_type = ModuleType.objects.create(manufacturer=manufacturer, model='Test Module Type')
+        bay1 = ModuleBay.objects.create(device=device, name='Test Bay 1')
+        bay2 = ModuleBay.objects.create(device=device, name='Test Bay 2')
+
+        # Install a module in bay1
+        module1 = Module.objects.create(device=device, module_bay=bay1, module_type=module_type)
+
+        # Assign bay2 to module1 and verify parent is now set to bay1 (module1's bay)
+        bay2.module = module1
+        bay2.save()
+        bay2.refresh_from_db()
+        self.assertEqual(bay2.parent, bay1)
+        self.assertEqual(bay2.module, module1)
+
+        # Clear the module assignment (return bay2 to device level) Verify parent is cleared
+        bay2.module = None
+        bay2.save()
+        bay2.refresh_from_db()
+        self.assertIsNone(bay2.parent)
+        self.assertIsNone(bay2.module)
+
 
 class CableTestCase(TestCase):