You've Got Mail

Kathleen Kelly is involved with Frank Navasky, a leftist postmodernist newspaper writer for The New York Observer who is always in search of an opportunity to root for the underdog. While Frank is devoted to his typewriter, Kathleen prefers her laptop and logging into her AOL email account. Using the screen name 'Shopgirl', she reads an email from "NY152", the screen name of Joe Fox whom she first met in an "over-30s" chatroom. As her voice narrates her reading of the email, she reveals the boundaries of the online relationship; no specifics, including no names, career or class information, or family connections. Joe belongs to the Fox family which runs Fox Books â a chain of mega bookstores. Kathleen runs the independent bookstore "The Shop Around The Corner" that her mother ran before her. The two are shown passing each other on their respective ways to work, revealing that they frequent the same neighborhoods in upper west Manhattan. Joe arrives at work, overseeing the opening of a new Fox Books in New York City with the help of his best friend, branch manager Kevin. Kathleen and her three store assistants, George, Aunt Birdie and Christina open up her small shop that morning.
Following a day with his eleven-year-old aunt Annabel and four-year-old half brother Matthew, Joe enters Kathleen's store to let his younger relatives experience story time. Joe and Kathleen have a conversation that reveals Kathleen's fears about the Fox Books store opening around the corner. He omits his last name and makes an abrupt exit with the children. At a publishing party for New York book business people later that week, Joe and Kathleen meet again, where Kathleen discovers Joe's true identity. She accuses him of deception and spying, while he responds by belittling her store.
The Shop Around the Corner slowly goes under. Kathleen enters Fox Books to discover the true nature of the store is one of friendliness and relaxation, yet without the same dedication to children's books as her shop. Her employees move on to other jobs; as Christina goes job hunting, George gets a job at the children's department at a Fox Books store and Birdie retires.
They are exchanging emails without knowing each others' true identities -- and their respective significant-others' knowledge. In some chance meetings Fox at first conceals his identity and then they clash, without realizing who each is. When they decide to meet, Joe discovers who he has been corresponding with. At first deciding to not meet with her, but then to meet with her without revealing his on-line identity. But, they again clash. Joe soon resumes the correspondence, apologizes, and promises to eventually tell her why he stood her up.
After both break up with their significant others, Joe realizes his feelings towards Kelly, and begins building a face-to-face relationship, still keeping his on-line identity a secret. He arranges a meeting between Kelly and his on-line persona (along with his dog Brinkley), but just before she is to meet this on-line friend, he reveals his feelings for her. Upon arriving at the agreed meeting place, she hears Fox calling to Brinkley, who has run ahead, and sees that her on-line friend is really Fox, and that she loves him, too.

Question: Who is Joe's half brother?
Answer: Matthew