diff --git a/DigitalLearningSolutions.Data.Migrations/202410091524_UpdateCandidateAssessmentSupervisorsDuplicateRows.cs b/DigitalLearningSolutions.Data.Migrations/202410091524_UpdateCandidateAssessmentSupervisorsDuplicateRows.cs
new file mode 100644
index 0000000000..c17179482c
--- /dev/null
+++ b/DigitalLearningSolutions.Data.Migrations/202410091524_UpdateCandidateAssessmentSupervisorsDuplicateRows.cs
@@ -0,0 +1,24 @@
+namespace DigitalLearningSolutions.Data.Migrations
+{
+    using FluentMigrator;
+
+    [Migration(202410091524)]
+    public class UpdateCandidateAssessmentSupervisorsDuplicateRows : ForwardOnlyMigration
+    {
+        public override void Up()
+        {
+            Execute.Sql(@$"WITH CAS_Duplicates AS (
+                        SELECT ID,
+                            ROW_NUMBER() OVER (PARTITION BY CandidateAssessmentID,SupervisorDelegateId ORDER BY Id DESC) AS RowNum
+                        FROM CandidateAssessmentSupervisors
+	                    WHERE CandidateAssessmentSupervisors.Removed is null
+                    )
+                    UPDATE CandidateAssessmentSupervisors
+                    SET Removed = GETUTCDATE()
+                    FROM CandidateAssessmentSupervisors cas INNER JOIN 
+		                    CAS_Duplicates casd ON cas.ID = casd.ID
+                    WHERE casd.RowNum > 1;");
+        }
+
+    }
+}