diff --git a/doc/api/next_api_changes/removals/27968-ES.rst b/doc/api/next_api_changes/removals/27968-ES.rst
new file mode 100644
index 000000000000..99b3b1527506
--- /dev/null
+++ b/doc/api/next_api_changes/removals/27968-ES.rst
@@ -0,0 +1,14 @@
+``legend.legendHandles``
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+... was undocumented and has been renamed to ``legend_handles``.
+
+Passing undefined *label_mode* to ``Grid``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+... is no longer allowed. This includes `mpl_toolkits.axes_grid1.axes_grid.Grid`,
+`mpl_toolkits.axes_grid1.axes_grid.AxesGrid`, and
+`mpl_toolkits.axes_grid1.axes_grid.ImageGrid` as well as the corresponding classes
+imported from `mpl_toolkits.axisartist.axes_grid`.
+
+Pass ``label_mode='keep'`` instead to get the previous behavior of not modifying labels.
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
index 111e08e00869..9033fc23c1a1 100644
--- a/lib/matplotlib/legend.py
+++ b/lib/matplotlib/legend.py
@@ -633,9 +633,6 @@ def __init__(
         else:
             raise ValueError(f"Invalid labelcolor: {labelcolor!r}")
 
-    legendHandles = _api.deprecated('3.7', alternative="legend_handles")(
-        property(lambda self: self.legend_handles))
-
     def _set_artist_props(self, a):
         """
         Set the boilerplate props for artists added to Axes.
diff --git a/lib/matplotlib/legend.pyi b/lib/matplotlib/legend.pyi
index d559b06c5d5d..dde5882da69d 100644
--- a/lib/matplotlib/legend.pyi
+++ b/lib/matplotlib/legend.pyi
@@ -150,5 +150,3 @@ class Legend(Artist):
         update: Literal["loc", "bbox"] = ...,
     ) -> None: ...
     def get_draggable(self) -> bool: ...
-    @property
-    def legendHandles(self) -> list[Artist | None]: ...
diff --git a/lib/mpl_toolkits/axes_grid1/axes_grid.py b/lib/mpl_toolkits/axes_grid1/axes_grid.py
index 720d985414ff..1c4551092c24 100644
--- a/lib/mpl_toolkits/axes_grid1/axes_grid.py
+++ b/lib/mpl_toolkits/axes_grid1/axes_grid.py
@@ -234,6 +234,7 @@ def set_label_mode(self, mode):
             - "all": All axes are labelled.
             - "keep": Do not do anything.
         """
+        _api.check_in_list(["all", "L", "1", "keep"], mode=mode)
         is_last_row, is_first_col = (
             np.mgrid[:self._nrows, :self._ncols] == [[[self._nrows - 1]], [[0]]])
         if mode == "all":
@@ -244,15 +245,6 @@ def set_label_mode(self, mode):
         elif mode == "1":
             bottom = left = is_last_row & is_first_col
         else:
-            # Use _api.check_in_list at the top of the method when deprecation
-            # period expires
-            if mode != 'keep':
-                _api.warn_deprecated(
-                    '3.7', name="Grid label_mode",
-                    message='Passing an undefined label_mode is deprecated '
-                            'since %(since)s and will become an error '
-                            '%(removal)s. To silence this warning, pass '
-                            '"keep", which gives the same behaviour.')
             return
         for i in range(self._nrows):
             for j in range(self._ncols):
diff --git a/lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py b/lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py
index b1a18d77747e..56f07c026b97 100644
--- a/lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py
+++ b/lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py
@@ -432,13 +432,10 @@ def test_image_grid_single_bottom():
     grid.cbar_axes[0].colorbar(im)
 
 
-def test_image_grid_label_mode_deprecation_warning():
-    imdata = np.arange(9).reshape((3, 3))
-
+def test_image_grid_label_mode_invalid():
     fig = plt.figure()
-    with pytest.warns(mpl.MatplotlibDeprecationWarning,
-                      match="Passing an undefined label_mode"):
-        grid = ImageGrid(fig, (0, 0, 1, 1), (2, 1), label_mode="foo")
+    with pytest.raises(ValueError, match="'foo' is not a valid value for mode"):
+        ImageGrid(fig, (0, 0, 1, 1), (2, 1), label_mode="foo")
 
 
 @image_comparison(['image_grid.png'],