Nearly a week after David Letterman made a joke about Sarah Palin's daughter, the Late Show host admits it was a bad line and that he is sorry.

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During the taping of Monday's show, Letterman explains that the risque joke -- that Palin's daughter got "knocked up" by Alex Rodriguez during their recent trip to New York's Yankee Stadium -- thought by some to have targeted Palin's underage daughter, Willow, was actually intended for 18-year-old Bristol. The name of the daughter wasn't mentioned in the joke, which was part of Letterman's monologue on last Tuesday's show.

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"It's not your fault that it was misunderstood," he tells his audience. "It's my fault." He says he will try to do better in the future.

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Although Letterman clarified the mixup on his show last Wednesday, the Alaska governor lashed out at Letterman on Friday while visiting the Today show. She claimed he owed an apology to "young women across the country" for making the lewd joke.

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