Once upon a time, there were two separate worlds. And like all separate worlds these coexisted harmoniously until a single event split them permanently onto parallel tracks that would never again meet, allowing each world to grow independently of the other, becoming more and more vastly dissimilar as time went on. The crux of these two worlds, that moment when they first split, occurred in the rather extraordinary great hall of a rather extraordinary school in Scotland, where a man gazed upon the form of a small boy.

This man was named Severus Snape. He was a bitter man. A spy who had seen and done much wrong. He was also a man who had lost the woman he loved to the man who had tormented him in his already-miserable childhood. And the boy whom he watched was the product of that union.

And up to the break in the continuum, Severus Snape’s thoughts were these…

Severus Snape looked down a long, hooked nose at the cowering first years. His black eyes settled on a particularly scrawny specimen and, in a conditioned response that would have made Pavlov proud, felt a surge of animosity at the sight of a perfect replica of his childhood nemesis. Slight build, check. Disgracefully messy black hair, check. Ridiculous knobby knees, check. Black, round-rimmed wire glasses, check. Arrogant, hazel eyes…

The boy he had been scrutinizing suddenly looked up, his eyes locking on those of the surly professor, and Severus Snape barely suppressed a gasp.

Lily.

Only years of spywork allowed Snape to retain his composure as he casually broke eye contact. Damn him. He had her eyes. Her beautiful, shimmering, emerald green eyes shone out of the wretched, arrogant face of James Potter. Snape’s mind screamed its indignation. Did he really have to spend the next seven years gazing upon this reminder of his mistakes, the proof that the woman he loved had married…had loved…the man whom he had hated?

The child his Lily had give her life to save?

Rage broiled dangerously beneath his cool façade. She had been his Lily, damn it. She was his best friend long before she even met Potter. Merlin, she had hated Potter before sixth year. What right did James Potter have to sweet, caring, radiant Lily? With his arrogance, his cruelty, his self-serving ways, what right did he have to her as his wife? What gave him the right to have her in his bed? To have her be the mother of his child?

His child.

He searched again for that messy mop of hair, but did not see the boy. His mind only showed him the ghosts of long-buried memories. He had loved her. Always loved her. Would have done anything for her. She should have been his. She should have been his wife. She should have shared his bed. The boy should have been his child.

His child.

Here is where the world splits. In one universe, the knowledge of that lost opportunity fills Severus Snape with a powerful bitterness. He takes the opportunity, the next time the child looks at him, to scowl darkly. He spends the next several years punishing the boy for the sins of his father, while simultaneously protecting him for the memory of his mother. Eventually, Snape meets his end, staring into eyes that remind him of his long lost love, alone in all the ways that count and with a heart filled with regret. Blood, venom, and memories, the things that wholly constituted his life, pooled around his dying body.

But that story has already been told, and is in fact not mine to tell.

My story is that of the second universe that arose from that split, and in that second universe, events unfurled quite differently.

…The boy should have been his child.

His child.

And he’d be damned if he was going to have something of his taken from him again. Snape smirked. It was high time that James Potter, the spoiled sod that he was, even dead, had something precious taken from him.

He would roll in his grave to see his heir look to Snivellus for guidance. James Potter’s son would be the son that should have been his…His child with his beloved Lily Evans. The ultimate revenge. He would steal the boy’s love away from that bastard who’d stolen hers from him.

His decision made, he immediately put all of his Slytherin cunning to a plan. And when the boy met his gaze again, Severus Snape did something he had not done in many, many years. He smiled warmly at the boy he was determined to make his own.

Fleetingly, and with a hint of confusion, Harry James Potter smiled back.