Say It Isn't So (2001)

Boy meets girl; boy falls in love (and had wild, non-stop sex) with girl; boy loses girl... when they discover they are brother and sister! But when he learns that he's the victim of the ultimate case of mistaken identity, the lovesick young man -- whom everyone still thinks is after some taboo thrills -- must race across the country to stop her from marrying another man.

Crew: J.B. Rogers

Cast: Chris Klein, Heather Graham, Orlando Jones, Sally Field, Richard Jenkins

Format: DVD

Genre: Comedy, Romance

Rating: M

More information (TMDB)