diff --git Lib/argparse.py Lib/argparse.py
index b44fa4f0f6..53310b95be 100644
--- Lib/argparse.py
+++ Lib/argparse.py
@@ -1437,7 +1437,7 @@ def add_argument(self, *args, **kwargs):
 
         return self._add_action(action)
 
-    def add_argument_group(self, *args, **kwargs):
+    def _add_argument_group(self, *args, **kwargs):
         group = _ArgumentGroup(self, *args, **kwargs)
         self._action_groups.append(group)
         return group
@@ -1635,6 +1635,7 @@ def __init__(self, container, title=None, description=None, **kwargs):
         self._has_negative_number_optionals = \
             container._has_negative_number_optionals
         self._mutually_exclusive_groups = container._mutually_exclusive_groups
+        self._container = container
 
     def _add_action(self, action):
         action = super(_ArgumentGroup, self)._add_action(action)
@@ -1645,13 +1646,21 @@ def _remove_action(self, action):
         super(_ArgumentGroup, self)._remove_action(action)
         self._group_actions.remove(action)
 
+    def add_argument_group(self, *args, **kwargs):
+        if isinstance(self, _ArgumentGroup) and not isinstance(self, _MutuallyExclusiveGroup):
+            from warnings import warn
+            warn('Adding an argument group to another group is deprecated, and not supported', DeprecationWarning, stacklevel=2)
+            # actions are added to the correct object with properly printed help
+            return self
+        else:
+            return super()._add_argument_group(self, *args, **kwargs)
+
 
 class _MutuallyExclusiveGroup(_ArgumentGroup):
 
     def __init__(self, container, required=False):
         super(_MutuallyExclusiveGroup, self).__init__(container)
         self.required = required
-        self._container = container
 
     def _add_action(self, action):
         if action.required:
@@ -1665,6 +1674,15 @@ def _remove_action(self, action):
         self._container._remove_action(action)
         self._group_actions.remove(action)
 
+    add_argument_group = _ArgumentGroup._add_argument_group
+
+    def add_mutually_exclusive_group(self, *args, **kwargs):
+        if isinstance(self._container, _MutuallyExclusiveGroup):
+            from warnings import warn
+            warn('Adding a mutually exclusive group to another  mutually exclusive group  is deprecated, and not supported',
+                  DeprecationWarning, stacklevel=2)
+
+        return super()._add_argument_group(self, *args, **kwargs)
 
 class ArgumentParser(_AttributeHolder, _ActionsContainer):
     """Object for parsing command line strings into Python objects.
@@ -1750,6 +1768,8 @@ def identity(string):
             else:
                 self._defaults.update(defaults)
 
+    add_argument_group = _ActionsContainer._add_argument_group
+
     # =======================
     # Pretty __repr__ methods
     # =======================