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Talk show legend David Letterman took Julia Roberts by surprise after he "double flipped-off" his audience live on air during "The Late Show," and RadarOnline.com has the video.

The "Larry Crowne" star -- who is one of Letterman's favorite celebrities -- gasped after she realized he had given the crowd the two-fingered salute.

It happened after Letterman explained to the Oscar winner how his biggest sadness in life was that his son did not have a brother or sister.

When the audience interrupted his conversation with a half-hearted, "aww," he let them have the "double bird" to show his disapproval.

Roberts, 43, has three kids with her husband Danny Moder: twins Hazel and Phinnaeus (both 6) and a son Henry, 4.

Letterman, 64, has a son Harry, 8, with his wife Regina Lasko.

Several years ago Letterman infamously did an inverted single flip-off to a viewer who sent him a letter claiming he watched the show upside down so that blood could rush to his head.

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