diff --git a/keystone/trust/backends/base.py b/keystone/trust/backends/base.py
index 4e11979253..557268926a 100644
--- a/keystone/trust/backends/base.py
+++ b/keystone/trust/backends/base.py
@@ -79,3 +79,19 @@ class TrustDriverBase(object):
 
         """
         raise exception.NotImplemented()  # pragma: no cover
+
+    @abc.abstractmethod
+    def flush_expired_and_soft_deleted_trusts(self, project_id=None,
+                                              trustor_user_id=None,
+                                              trustee_user_id=None,
+                                              date=None):
+        """Flush expired and non-expired soft deleted trusts from the backend.
+
+        :param project_id: ID of a project to filter trusts by.
+        :param trustor_user_id: ID of a trustor_user_id to filter trusts by.
+        :param trustee_user_id: ID of a trustee_user_id to filter trusts by.
+        :param date: date to filter trusts by.
+        :type date: datetime
+
+        """
+        raise exception.NotImplemented()  # pragma: no cover
diff --git a/releasenotes/notes/bug-1473292-c21481e6aec29ec2.yaml b/releasenotes/notes/bug-1473292-c21481e6aec29ec2.yaml
index c35581187b..8228e59751 100644
--- a/releasenotes/notes/bug-1473292-c21481e6aec29ec2.yaml
+++ b/releasenotes/notes/bug-1473292-c21481e6aec29ec2.yaml
@@ -1,7 +1,7 @@
 ---
 feature:
   - |
-    [`Bug 1473292 <https://bugs.launchpad.net/keystone/+bug/1473292>`_]
+    [`bug 1473292 <https://bugs.launchpad.net/keystone/+bug/1473292>`_]
     As trusts created by user are stored in database resulting it to grow larger
     as trusts that are expired and soft deleted non-expired are not automatically
     purged by keystone.Thus this implements TrustFlush via keystone-manage to delete
@@ -18,6 +18,8 @@ feature:
         --trustee-user-id <string>: To purge trusts of given trustee-id.
         --date <string>: To purge trusts older than date. It will purge trusts older than
            current if date not given.
-
-
-
+other:
+  - >
+    [`bug 1473292 <https://bugs.launchpad.net/keystone/+bug/1473292>`_]
+    If you're relying on a custom implementation of the trust backend, please be sure to
+    implement the new method prior to upgrading.