BOSTON (CBS) – Filmmaker Rory Kennedy presented her newest movie at the Sundance Film Festival.

Her new HBO documentary is entitled “Ethel” and is about her mother, who is the widower of Senator Robert Kennedy.

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Rory Kennedy says making the documentary was difficult, since it was so personal.

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She says, “I think that one of the hardest parts for me beyond the kind of weight and responsibility of doing a documentary about my family is, is asking those questions of my mother and my siblings, there’s obviously a huge amount of sadness that has occurred and to ask people who are close to me to revisit those moments was very difficult. “

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The documentary will air on HBO later this year.