As he looked at the smoke rises swaying along with the breeze,so too are his hearts beating to the sound of drums in his head. When will this drumming ever stop? Everyday, every moment, for the past several hundred years, without fail, there is this drumbeat that only he can hear and feel. Hearing the drumbeat might be irritating, and he could easily shut it out, but it is the fact that his both hearts are beating along to the drumbeats that is gnawing at him.
He tried to force himself to regenerate by harming himself, but that did not work. He tried to stop one of his hearts with the hope that having two hearts is the cause, but that did not work either. He went to the best doctor in every galaxy in every time and still he could not find a solution to the drumming in his head.
And then he remembered that he could be human. Yet he did not want to defile his Time Lord nature by becoming just human. But there was no other choice, either he live with the drumming or he became human and hope for the best. Self preservation always comes first. Before he changed himself into human, he went to the end of the universe. At least if it fails and the drumming still continues, he would not have to endure long before everything vanishes into nothingness.
At the end of the universe, he picked a name. A name that he knew his oldest and only friend that he loved will figure out. He might be regarded as pure evil, but still, he chose a name that he knew would give his friend hope.
His last words as a Time Lord were, "Doctor, you are not alone."