diff --git a/ipykernel/zmqshell.py b/ipykernel/zmqshell.py
index f41bcfb70..34308ae5b 100644
--- a/ipykernel/zmqshell.py
+++ b/ipykernel/zmqshell.py
@@ -56,8 +56,6 @@
 # Functions and classes
 #-----------------------------------------------------------------------------
 
-_sentinel = object()
-
 
 class ZMQDisplayPublisher(DisplayPublisher):
     """A display publisher that publishes data using a ZeroMQ PUB socket."""
@@ -97,7 +95,6 @@ def publish(
         self,
         data,
         metadata=None,
-        source=_sentinel,
         transient=None,
         update=False,
     ):
@@ -115,23 +112,7 @@ def publish(
             Transient data should not be persisted to documents.
         update : bool, optional, keyword-only
             If True, send an update_display_data message instead of display_data.
-        source : unused
-            Value will have no effect on function behavior. Parameter is still
-            present for backward compatibility but will be removed in the
-            future.
-
-            .. deprecated:: 4.0.1
-
-                `source` has been deprecated and no-op since ipykernel 4.0.1
-                (2015)
         """
-        if source is not _sentinel:
-            warnings.warn(
-                "`source` has been deprecated since ipykernel 4.0.1 "
-                "and will have no effect",
-                DeprecationWarning,
-                stacklevel=2,
-            )
         self._flush_streams()
         if metadata is None:
             metadata = {}