I don’t know the people involved, they’re friends of my wife’s colleague, but I’ll make up some names to make it easier to describe:
Adam and Ben are 28, and have been good mates since they met at university, 10 years ago. They became such good friends, that Ben would regularly go round to Adam’s house during holidays and over the following years, getting to know his family in the process.
Adam has a younger sister, Clare. Clare is 18 years old. She first met Ben 10 years ago, when she was 8.