How did news of Mehri’s clandestine affair reach Marji’s father?

At the beginning of the revolution, in 1978, Mehri falls in love with the neighbor’s son. They begin to write letters to each other, but because Mehri is illiterate, Marjane has to write the letters for her. Mehri tells the boy that she often talks to her sister about him. Marjane asks who her sister is and Mehri tells her that she is her sister.

One day, Mehri talks with her real biological sister who works as a maid for Marjane’s uncle and tells her that she has a fiancé. Mehri’s sister becomes jealous and tells Marjane’s uncle who then tells her grandmother who tells her mother. Eventually the story comes to her father. Her father goes straight to their neighbor’s son. The boy is wearing a Bee Gee’s t-shirt when he answers the door. Mr. Satrapi tells the boy that Mehri is not really his daughter but is, instead, his maid. The boy decides that he does not want to continue seeing her and give Mr. Satrapi all the letters they had written to each other.