Now you only have your father and Yn and Sean only dated for 3 years secretly

One day your father came back to your house saying he now found a new lover and they're going to live with you with her son which is now going to be your stepbrother.

As you saw your new mother you gave her a hug and you both introduced yourself. After that his son now stepped inside your house.

There, you saw someone you've least expected to be your new step brother, Sean.