Using the analogue of TpT methylated at the 3'-end N-3 position (Tpm(3)T), we demonstrate that when the oxetane/(6-4) pathway is precluded, water addition occurs at the 3'-end C6 position of the oxetane intermediate to provide its opening. Photoreversal of this (6-4) photoproduct C6 hydrate brings the first experimental evidence that the (6-4) photolyase repair can proceed through an oxetane intermediate.