diff --git a/pytorch_lightning/loggers/comet.py b/pytorch_lightning/loggers/comet.py
index a98b2c7fa5..a4fca47923 100644
--- a/pytorch_lightning/loggers/comet.py
+++ b/pytorch_lightning/loggers/comet.py
@@ -188,7 +188,7 @@ class CometLogger(LightningLoggerBase):
 
     @property
     @rank_zero_experiment
-    def experiment(self):
+    def experiment(self) -> Union[CometExperiment, CometExistingExperiment, CometOfflineExperiment]:
         r"""
         Actual Comet object. To use Comet features in your
         :class:`~pytorch_lightning.core.lightning.LightningModule` do the following.