He has seen so many children die.
He can only watch, now, as the freighter descends, burning into nothing, leaving no trace of stubborn brilliance or youthful defiance.
Sometimes he can't stop it. Sometimes he lets it happen. Sometimes he orchestrates it. It is never right, and it is never fair.
It soon dawns on him that the doomed ship was destined to transform the Earth. There was no need to send him to stop it.
He does not allow himself to mourn. Remorse has no place in his mission, his quest for a better universe. Morality cannot be allowed to stand in his way.
"How could you?" An enraged whisper from quivering lips, and he turns away from her, turns toward the remaining threat.
The Doctor should feel only relentless determination, and just enough anger.
His hands tremble as he grips the stolen weapon, firing again and again until there is nothing left but black smoke and charred steel.
It does not matter that he was his student, his companion, his responsibility. He is now simply another sacrifice for the greater cause.
He drops the gun as the smoke clears, kneeling in silence to pocket a fallen star.