Castle on the Hill

A boy and a girl, about five years old, running around in their backyard, playing tag.
The same two, a year older, climbing up the treehouse that their father had built for them.
Two years later, playing hide and seek with their 6-year-old brother.
A year later, the girl crying in pain, while the boy yelled for their parents.
One more year later, the girl in her room playing with their brother, while the boy was being yelled at by their mother.
Finally when they were 11, standing on the platform as their parents kissed and hugged them goodbye. They weren't standing together. The twins' bond had been broken.

This is the story of Sirius and Rigel Black.