Lena Dunham's sister, Grace, defends sex stories

Lena Dunham issued a formal apology on Tuesday for describing herself as a "sexual predator" - in comic fashion - when it came to sister Grace in her memoir, Not that Kind of Girl.

The Girls star has been at the center of a controversy over passages in the book in which she details kissing her sister and looking at her private parts when they were little girls.

Lena also mentioned in her statement that Grace is her "best friend" and said nothing was written without Grace's approval.

Grace, 22, who came out as a lesbian to Lena during Grace's senior year in high school, has weighed in on Twitter in a series of comments in which she essentially says its up to her to decide what's harmful.

And, she says it's a good time to "think about how we police the sexuality of young women, queer and trans people."

Grace Dunham @simongdunham

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heteronormativity deems certain behaviours harmful, and others "normal"; the state and media are always invested in maintaining that

Grace Dunham @simongdunham

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2day, like every other day, is a good day to think about how we police the sexualities of young women, queer, and trans people

7:02 PM - 3 Nov 2014

Lena, who is on a book tour in Europe, has canceled appearances this week inBelgium and Germany.