--- a/chrome/browser/ungoogled_flag_entries.h
+++ b/chrome/browser/ungoogled_flag_entries.h
@@ -100,4 +100,8 @@
      "Disable Sharing Hub",
      "Disables the sharing hub button. ungoogled-chromium flag.",
      kOsDesktop, SINGLE_VALUE_TYPE("disable-sharing-hub")},
+    {"hide-sidepanel-button",
+     "Hide SidePanel Button",
+     "Hides the SidePanel Button. ungoogled-chromium flag.",
+     kOsDesktop, SINGLE_VALUE_TYPE("hide-sidepanel-button")},
 #endif  // CHROME_BROWSER_UNGOOGLED_FLAG_ENTRIES_H_
