At the end of time, Donna's grandfather accidentally entered a device, and another person had to turn it on. The doctor was struggling at the time, because if he opened it, he would die. When it is opened, it will release something (forget what it is), which will lead to the death of life. After opening it, the doctor had a sharp pain at first, but later he recovered and the injury healed. Means that rebirth is about to begin. After bidding farewell to his friends, the doctor was reborn in his own Tadis. It became 1 1 (matt smith)