diff --git a/Lib/test/test_tstring.py b/Lib/test/test_tstring.py
index ea20688fdc9753..4cbe0b178f1c35 100644
--- a/Lib/test/test_tstring.py
+++ b/Lib/test/test_tstring.py
@@ -435,5 +435,14 @@ def test_triple_quoted(self):
         t = t'''{f"{d["a#b"]}"}'''
         self.assertEqual(t.interpolations[0].expression, 'f"{d["a#b"]}"')
 
+    def test_not_equal_with_format_spec(self):
+        # gh-146448: != in expression with format spec should not be
+        # confused with the ! conversion specifier
+        t = t"{0!=0:}"
+        self.assertTStringEqual(t, ("", ""), [(False, "0!=0")])
+
+        t = t"{0!=0:s}"
+        self.assertTStringEqual(t, ("", ""), [(False, "0!=0", None, "s")])
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-03-30-00-00-00.gh-issue-146448.5fce3b.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-03-30-00-00-00.gh-issue-146448.5fce3b.rst
new file mode 100644
index 00000000000000..40a19df9bd0a99
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-03-30-00-00-00.gh-issue-146448.5fce3b.rst
@@ -0,0 +1,2 @@
+Fix template string parser incorrectly truncating the ``Interpolation.str``
+attribute when the expression contains ``!=`` followed by a format spec.