He hated the boy's face.
It belonged to the only man he had ever really hated.
Every time he saw that face, he felt a strong desire to kill the boy, if only to get rid of that face.
That face that laughed and mocked and hexed without a care.
That face that talked to her, kissed her, said "I do" to her.
That face that took everything from him.
He had thought, now that the man was dead, the face that tortured him would go away.
But it came back with this stupid, arrogant boy who was just as useless as his father had been.
Another Quidditch player, another dunce, another hothead.
The man had found a way to tease him from beyond the grave. He was always inventive.
He decided the boy would suffer like he had. That he would do everything he could to make that man's son miserable.
And he did.
DISCLAIMER: Still not J.K. Rowling. It makes me sad.