diff --git a/app/controllers/delete_logs_controller.rb b/app/controllers/delete_logs_controller.rb
index 23579ed6b..561fe7346 100644
--- a/app/controllers/delete_logs_controller.rb
+++ b/app/controllers/delete_logs_controller.rb
@@ -25,6 +25,7 @@ class DeleteLogsController < ApplicationController
 
   def discard_lettings_logs
     logs = LettingsLog.find(params.require(:ids))
+    remove_lettings_duplicate_set_ids(logs)
     discard logs
     if request.referer&.include?("delete-duplicates")
       logs.each do |log|
@@ -59,6 +60,7 @@ class DeleteLogsController < ApplicationController
 
   def discard_sales_logs
     logs = SalesLog.find(params.require(:ids))
+    remove_sales_duplicate_set_ids(logs)
     discard logs
     if request.referer&.include?("delete-duplicates")
       logs.each do |log|
@@ -213,4 +215,30 @@ private
   def duplicate_log_ids(logs)
     logs.map { |log| "Log #{log.id}" }.to_sentence(last_word_connector: " and ")
   end
+
+  def remove_lettings_duplicate_set_ids(logs)
+    duplicate_set_ids = []
+    logs.each do |log|
+      if log.duplicate_set_id.present?
+        duplicate_set_ids << log.duplicate_set_id
+        log.update!(duplicate_set_id: nil)
+      end
+    end
+    duplicate_set_ids.uniq.each do |duplicate_set_id|
+      LettingsLog.where(duplicate_set_id:).update!(duplicate_set_id: nil) if LettingsLog.where(duplicate_set_id:).count == 1
+    end
+  end
+
+  def remove_sales_duplicate_set_ids(logs)
+    duplicate_set_ids = []
+    logs.each do |log|
+      if log.duplicate_set_id.present?
+        duplicate_set_ids << log.duplicate_set_id
+        log.update!(duplicate_set_id: nil)
+      end
+    end
+    duplicate_set_ids.uniq.each do |duplicate_set_id|
+      SalesLog.where(duplicate_set_id:).update!(duplicate_set_id: nil) if SalesLog.where(duplicate_set_id:).count == 1
+    end
+  end
 end
diff --git a/spec/requests/delete_logs_controller_spec.rb b/spec/requests/delete_logs_controller_spec.rb
index cfb8bb069..58ccae200 100644
--- a/spec/requests/delete_logs_controller_spec.rb
+++ b/spec/requests/delete_logs_controller_spec.rb
@@ -247,6 +247,53 @@ RSpec.describe "DeleteLogs", type: :request do
         expect(log_2.discarded_at).to be nil
       end
     end
+
+    context "when an authorized user deletes a log that had duplicates" do
+      context "and only 1 log remains in the duplicate set" do
+        let!(:log_1) { create(:lettings_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_2) { create(:lettings_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_3) { create(:lettings_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+
+        it "deletes the log and marks related logs deduplicated" do
+          delete delete_logs_lettings_logs_path, params: params
+          log_1.reload
+          expect(log_1.status).to eq "deleted"
+          expect(log_1.discarded_at).not_to be nil
+          expect(log_1.duplicates.count).to eq(0)
+          expect(log_1.duplicate_set_id).to be nil
+          log_2.reload
+          expect(log_2.status).to eq "deleted"
+          expect(log_2.discarded_at).not_to be nil
+          expect(log_2.duplicates.count).to eq(0)
+          expect(log_2.duplicate_set_id).to be nil
+          log_3.reload
+          expect(log_3.duplicates.count).to eq(0)
+          expect(log_3.duplicate_set_id).to be nil
+        end
+      end
+
+      context "and multiple logs remains in the duplicate set" do
+        let!(:log_1) { create(:lettings_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_2) { create(:lettings_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_3) { create(:lettings_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let(:params) { { ids: [log_1.id] } }
+
+        it "deletes the log and marks related logs deduplicated" do
+          delete delete_logs_lettings_logs_path, params: params
+          log_1.reload
+          expect(log_1.status).to eq "deleted"
+          expect(log_1.discarded_at).not_to be nil
+          expect(log_1.duplicates.count).to eq(0)
+          expect(log_1.duplicate_set_id).to be nil
+          log_2.reload
+          log_3.reload
+          expect(log_2.duplicates.count).to eq(1)
+          expect(log_3.duplicates.count).to eq(1)
+          expect(log_3.duplicate_set_id).not_to be nil
+          expect(log_3.duplicate_set_id).to eq(log_2.duplicate_set_id)
+        end
+      end
+    end
   end
 
   describe "GET sales-logs/delete-logs" do
@@ -487,6 +534,53 @@ RSpec.describe "DeleteLogs", type: :request do
         expect(log_2.discarded_at).to be nil
       end
     end
+
+    context "when an authorized user deletes a log that had duplicates" do
+      context "and only 1 log remains in the duplicate set" do
+        let!(:log_1) { create(:sales_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_2) { create(:sales_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_3) { create(:sales_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+
+        it "deletes the log and marks related logs deduplicated" do
+          delete delete_logs_sales_logs_path, params: params
+          log_1.reload
+          expect(log_1.status).to eq "deleted"
+          expect(log_1.discarded_at).not_to be nil
+          expect(log_1.duplicates.count).to eq(0)
+          expect(log_1.duplicate_set_id).to be nil
+          log_2.reload
+          expect(log_2.status).to eq "deleted"
+          expect(log_2.discarded_at).not_to be nil
+          expect(log_2.duplicates.count).to eq(0)
+          expect(log_2.duplicate_set_id).to be nil
+          log_3.reload
+          expect(log_3.duplicates.count).to eq(0)
+          expect(log_3.duplicate_set_id).to be nil
+        end
+      end
+
+      context "and multiple logs remains in the duplicate set" do
+        let!(:log_1) { create(:sales_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_2) { create(:sales_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let!(:log_3) { create(:sales_log, :duplicate, duplicate_set_id: 5, created_by: user) }
+        let(:params) { { ids: [log_1.id] } }
+
+        it "deletes the log and marks related logs deduplicated" do
+          delete delete_logs_sales_logs_path, params: params
+          log_1.reload
+          expect(log_1.status).to eq "deleted"
+          expect(log_1.discarded_at).not_to be nil
+          expect(log_1.duplicates.count).to eq(0)
+          expect(log_1.duplicate_set_id).to be nil
+          log_2.reload
+          log_3.reload
+          expect(log_2.duplicates.count).to eq(1)
+          expect(log_3.duplicates.count).to eq(1)
+          expect(log_3.duplicate_set_id).not_to be nil
+          expect(log_3.duplicate_set_id).to eq(log_2.duplicate_set_id)
+        end
+      end
+    end
   end
 
   context "when a support user navigates to the organisations tab" do