diff --git a/lib/cooked_post_processor.rb b/lib/cooked_post_processor.rb
index 8651502c8f7..d96d81f6836 100644
--- a/lib/cooked_post_processor.rb
+++ b/lib/cooked_post_processor.rb
@@ -621,7 +621,16 @@ class CookedPostProcessor
     end
 
     if @omit_nofollow || !SiteSetting.add_rel_nofollow_to_user_content
-      @doc.css(".onebox-body a, .onebox a").each { |a| a.remove_attribute("rel") }
+      @doc.css(".onebox-body a[rel], .onebox a[rel]").each do |a|
+        rel_values = a['rel'].split(' ').map(&:downcase)
+        rel_values.delete('nofollow')
+        rel_values.delete('ugc')
+        if rel_values.blank?
+          a.remove_attribute("rel")
+        else
+          a["rel"] = rel_values.join(' ')
+        end
+      end
     end
   end
 
diff --git a/spec/components/cooked_post_processor_spec.rb b/spec/components/cooked_post_processor_spec.rb
index fef1e06aa3c..9164a7a4786 100644
--- a/spec/components/cooked_post_processor_spec.rb
+++ b/spec/components/cooked_post_processor_spec.rb
@@ -1102,13 +1102,13 @@ describe CookedPostProcessor do
       SiteSetting.add_rel_nofollow_to_user_content = false
       Oneboxer.expects(:onebox)
         .with("http://www.youtube.com/watch?v=9bZkp7q19f0", invalidate_oneboxes: true, user_id: nil, category_id: post.topic.category_id)
-        .returns('<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0" rel="nofollow noopener">GANGNAM STYLE</a></aside>')
+        .returns('<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0" rel="nofollow noopener ugc">GANGNAM STYLE</a></aside>')
       cpp.post_process_oneboxes
     end
 
     it "removes nofollow noopener from links" do
       expect(cpp).to be_dirty
-      expect(cpp.html).to match_html '<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0">GANGNAM STYLE</a></aside>'
+      expect(cpp.html).to match_html '<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0" rel="noopener">GANGNAM STYLE</a></aside>'
     end
   end
 
@@ -1123,13 +1123,13 @@ describe CookedPostProcessor do
       SiteSetting.tl3_links_no_follow = false
       Oneboxer.expects(:onebox)
         .with("http://www.youtube.com/watch?v=9bZkp7q19f0", invalidate_oneboxes: true, user_id: nil, category_id: post.topic.category_id)
-        .returns('<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0" rel="nofollow noopener">GANGNAM STYLE</a></aside>')
+        .returns('<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0" rel="nofollow ugc noopener">GANGNAM STYLE</a></aside>')
       cpp.post_process_oneboxes
     end
 
-    it "removes nofollow noopener from links" do
+    it "removes nofollow ugc from links" do
       expect(cpp).to be_dirty
-      expect(cpp.html).to match_html '<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0">GANGNAM STYLE</a></aside>'
+      expect(cpp.html).to match_html '<aside class="onebox"><a href="https://www.youtube.com/watch?v=9bZkp7q19f0" rel="noopener">GANGNAM STYLE</a></aside>'
     end
   end