Billy Van Arsdale is born in New York in 1935. His family makes a fortune selling citrus juice for many businessmen, including Vito Corleone. He meets Vito Corleone's granddaughter, Francesca, in college in 1955; they are married a couple of years later after Francesca gives birth to their son, William Brewster Van Arsdale IV, whom they call 'Sonny', after Francesca's late father, Santino "Sonny" Corleone. Van Arsdale starts working as a Law Assistant in the Attorney General's office after graduation, due to his family connections. Shortly after, it is revealed that he has secretly been collecting evidence against the Corleone Family, most likely due to his grudge against Michael Corleone who he had his leg broken for infidelity.
By 1961, he begins an affair with one of Danny Shea's secretaries. Francesca never knows about this and believes he will not have sex with her because she is pregnant. In early 1962, Francesca learns about her husband's infidelity and his spying on her family. Distraught, she follows him in his own car one night. She finds him drunkenly stumbling out of a local bar, and runs him down in a fit of rage, literally cutting his body in half. She leaves the scene and calls her Uncle Michael for help.
It is later revealed that Van Arsdale's mistress is eventually convicted of second-degree murder for his death; it is implied that the Corleone family framed her to protect Francesca.