Letterman said it was his fault the joke had been misunderstood
US talk show host David Letterman has apologised for making a joke about one of Alaska Governor Sarah Palin's teenage daughters.
Mrs Palin complained after he joked on his show that a baseball player had "knocked up" one of her daughters.
Critics thought the joke was targeted at her 14-year-old daughter, Willow, but Letterman has now said it was about her sister Bristol, 18.
"I'm sorry about it and I'll try to do better in the future," he said.
Letterman made the joke last week after the governor took her family to watch a New York Yankees game.
Mrs Palin's husband, Todd, issued a statement describing the joke as "despicable" while the governor charged Letterman with "sexually perverted comments".
Letterman told viewers on Monday night: "I told a joke that was beyond flawed, and my intent is completely meaningless compared to the perception.
"I would like to apologise especially to the two daughters involved, Bristol and Willow, and also to the governor and her family and everybody else who was outraged by the joke.
"But I never thought it was [about] anybody other than the older daughter, and before the show I checked to make sure, in fact, that she is of legal age, 18.
"It's not your fault that it was misunderstood, it's my fault that it was misunderstood," he added.
A group of Palin supporters, calling themselves Fire David Letterman, is planning a protest outside the show's studio at the Ed Sullivan Theater in New York's Times Square on Tuesday.
Mrs Palin has accepted Letterman's apology, saying she hopes it will help change attitudes about men who joke about the sexual exploitation of young girls.