More than 70 years after The Quiet Man reached theaters, one tiny moment between Maureen O’Hara and John Wayne still has fans searching for an answer. At the very end of the 1952 classic, O’Hara leans toward Wayne and whispers something into his ear. His startled reaction looks remarkably genuine—and according to the story behind the scene, it was.

Director John Ford reportedly gave O’Hara an unscripted line specifically to surprise Wayne. O’Hara initially refused because she considered the words too improper to say to “Duke.” She eventually agreed, but only on the condition that the actual words would never be revealed. Ford, Wayne and O’Hara kept the secret.

Fans continued asking O’Hara about the mysterious whisper for decades. One recollection of her response has her joking that only three knew the answer: herself, John Wayne and God—and neither she nor God was going to reveal it. Wayne died in 1979, while O’Hara died in 2015 without publicly providing the answer.

There have been countless guesses about what she said, with speculation that the mysterious line was risqué or suggestive. But no confirmed wording has ever emerged. Whatever Maureen O’Hara whispered that produced John Wayne’s unforgettable reaction appears to have gone with Hollywood’s legends to their graves.