Jan. 22, 2013 -- Robert De Niro seldom talks about his private life.
But the Oscar winner, 70, is now revealing intimate details about his late father, who was a gay artist.
"Remembering the Artist Robert De Niro Sr." is an HBO documentary about the actor's father and even reads passages from his father's journals, which detail how he left the "Godfather" star's mother after he realized he was gay, according to the Hollywood Reporter.
The movie is shot through the actor's point of view.
De Niro Sr. was part of post-World War II painters based in New York during the 1950's. His art lost popularity in the 1960's when pop art became all the rage. The actor even explains his father's depression in the film over his art's failures.
"I did this for him," De Niro said. "I wanted my younger kids -- who were born after he died -- to know what their grandfather did. I even kept his painting studio intact so they could see it."
The documentary was screened this week at the Sundance Film Festival and airs on HBO in June.