Tom Cruise went on the 'Late Show With David Letterman' on Monday night expecting to promote his film 'Jack Reacher,' but instead ending up discussing the birds and the bees with Dave -- who dropped the F-bomb on the shocked actor.

The two fathers chatted about having the sex talk with their sons – because who wouldn't want to embarrass their kids on national television when given the opportunity – and that turned into a joke on Letterman's end about curse words.

Dave told Cruise his son Harry admitted to knowing the S-word, the B-word, and the F-word. Shocked, Letterman asked the 9-year-old what all those words were.

Harry said the S-word was "stupid" and the B-word was "bad." But when his relieved dad asked him what the F-word was, the boy matter-of-factly replied, “F---.”

Dear Harry: You're doing it right.

The naughty word was of course bleeped out (or in this case, honked out) by CBS, and as Cruise laughed, Letterman comically wished the audience good night.

“I'm sure someone's got the plug and they're pulling it,” Cruise joked.

Then an alien flew out of a volcano and swept Tom to safety.

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