It’s one of the most famous scenes in cinema history. Private Detective, Jake Gittes, is attempting to force the truth out of his lovely but damaged client, Evelyn Mulwray. Just who is the mysterious teenager everyone’s searching for?

Evelyn: She’s my daughter. [Gittes slaps Evelyn]

Gittes: I said I want the truth!

Evelyn: She’s my sister. . . . [slap]

Evelyn: She’s my daughter. . . . [slap]

Evelyn: My sister, my daughter. [More slaps]

Gittes: I said I want the truth!

[Jake throws Evelyn across the room]

Evelyn: She’s my sister and my daughter!

The film is Chinatown, a classic neo-noir widely regarded as one of the greatest films of the 1970s. A famously troubled production, screenwriter Robert Towne, director Roman Polanski, and producer Robert Evans eventually saved the film. It’s a brilliantly constructed mystery involving personal and political treachery in 1930s Los Angeles. Jack Nicholson’s performance as Jake Gittes ranks among his best.

Turns out, Gittes wasn’t the only one to discover a staggering revelation about family secrets and lies, and paternity. Just before the film’s release – in June 1974 – Nicholson received a shocking bit of news that uncannily reflected the iconic scene between Gittes and Evelyn Mulwray. Researchers for a Time magazine story discovered that the woman Nicholson thought was his sister was actually his mother. And the woman he’d thought was his mother was, in truth, his grandmother.

Nicholson was stunned. By that time, both women were dead, but his brother-in-law reluctantly confirmed the truth of the situation. Already a star, Nicholson asked Time to keep his family secret just that – a secret. But who can keep a juicy secret like this?

The devilish actor with the wolfish grin ultimately came to grips with the matter. “I’d say it was a pretty dramatic event, but it wasn’t what I’d call traumatizing. After all, by the time I found out who my mother was, I was pretty well psychologically formed. As a matter of fact, it made quite a few things clearer to me. If anything, I felt grateful.”

Chinatown remains a vivid and engrossing examination of crime, power, and corruption in the City of Angels. But sometimes the greatest mysteries are the ones closest to home.

Just ask Jack.