Writer, actor, singer, song writer, and talk show host Jimmy Fallon (born James Thomas Fallon Jr. on September 19, 1974 in Brooklyn, New York) does not have a brother, but he does have a sister.
Gloria Fallon is a freelance writer; she's named after their mother, just like Jimmy was named after their father (yes, Gloria and James Fallon have children named Gloria and James)
Jimmy and his sister wrote a book together: i hate this place: The Pessimist's Guide to Life; it's described as "a delightfully cynical look at life through a half-full glass."
Jimmy just had a fantastic Prime Time Special on NBC, an hour long broadcast of some of his best musical moments from his late night talk show. Parodies from Jim Morrison belting out the Reading Rainbow, to Bob Dylan singing the theme to Charles in Charge were some of the "must see to believe" sketches.