Say It Isn't So (2001)

Name: Say It Isn't So
Released: 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.

Genres: Comedy, Romance

What to watch after Say It Isn't So

Hope Springs (2003)
Rumor Has It... (2005)
Gray Matters (2006)
Stuck on You (2003) — Bobby Farrelly and Peter Farrelly produced both
Behaving Badly (2014) — Same feel: fun, irreverent
Isn't It Romantic (2019)