diff --git a/homeassistant/components/tplink/diagnostics.py b/homeassistant/components/tplink/diagnostics.py
index 5771bee5bd3..5121def2e47 100644
--- a/homeassistant/components/tplink/diagnostics.py
+++ b/homeassistant/components/tplink/diagnostics.py
@@ -36,11 +36,6 @@ async def async_get_config_entry_diagnostics(
 ) -> dict[str, Any]:
     """Return diagnostics for a config entry."""
     coordinator: TPLinkDataUpdateCoordinator = hass.data[DOMAIN][entry.entry_id]
-    device = coordinator.device
-
-    data = {}
-    data[
-        "device_last_response"
-    ] = device._last_update  # pylint: disable=protected-access
-
-    return async_redact_data(data, TO_REDACT)
+    return async_redact_data(
+        {"device_last_response": coordinator.device.internal_state}, TO_REDACT
+    )
diff --git a/tests/components/tplink/test_diagnostics.py b/tests/components/tplink/test_diagnostics.py
index d09ea72b70a..55dd1cee9c7 100644
--- a/tests/components/tplink/test_diagnostics.py
+++ b/tests/components/tplink/test_diagnostics.py
@@ -38,7 +38,7 @@ async def test_diagnostics(
     """Test diagnostics for config entry."""
     diagnostics_data = json.loads(load_fixture(fixture_file, "tplink"))
 
-    mocked_dev._last_update = diagnostics_data["device_last_response"]
+    mocked_dev.internal_state = diagnostics_data["device_last_response"]
 
     config_entry = await initialize_config_entry_for_device(hass, mocked_dev)
     result = await get_diagnostics_for_config_entry(hass, hass_client, config_entry)