(CNN) -- Barack Obama's father was more abusive and violent than the president was aware of, according to his half-brother, who has written a memoir about their father.
Mark Obama Ndesandjo, who is several years younger than the President, described their father as a brilliant man. But he was also an alcoholic, a "social failure" and an abusive husband, he said.
"I remember the sounds of my mothers' screams and I remember the sounds of breaking, things breaking," he told CNN. "And I remember that I couldn't protect her. That's something that no child ever forgets."
He said he especially remembered a violent episode when he was 6 or 7.
"My father actually broke -- came in the door, against the restraining order, and held a knife to my mother's throat," he said.
Barack Obama apparently met their father once because his parents got divorced soon after he was born. Ndesandjo and the president have the same father, but Obama's mother was the second wife while Ndesandjo's mother was his third wife.
Unlike Obama, Ndesandjo grew up with his father.
The president is lucky he never lived with his father, according to David Maraniss, author of "Barack Obama: The Story."
"It would have been a much more difficult upbringing," he said.
Divergent views of family history have caused some strain among Obama relatives, according to Ndesandjo.
"Barack I don't think accepts -- or at least does not want to know -- the details of the beatings that occurred in our family," he said. "I love my brother. He's a great president. Sometimes he's a lousy brother."
The White House did not respond to e-mails and phone calls Thursday about the president's half-brother's book. But in a 2009 interview with CNN, the president said he was not blind to the flaws of his father.
"It's no secret that my father was a troubled person. Anybody who has read my first book, "Dreams from My Father," knows that, you know, he had an alcoholism problem, that he didn't treat his families very well," he said. "Obviously it's a sad part of my history and my background. But it's not something that I spend a lot of time brooding over."
Ndesandjo and Obama have several things in common: similar good looks, biracial ethnicity, the same father and each had an American mother.
Despite their similarities, this is not the first time the two have been at odds.
When they first met in Kenya in the 1980s, Ndesandjo was growing up there and trying to connect with his American roots, he said.
At the time, Obama came from America and was "really looking for that African side of him, and was trying to find more about himself and his identity. And I respect that. But I also felt that there was a rejection of a lot of Western culture," Ndesandjo said.
"I felt that my brother -- at that time - felt that I was too white," he said. "And I thought he was too black."
When they first met, Ndesandjo said, his half-brother came on strong. "That imposing voice, and also that commanding presence -- he was almost like a barracuda with his questions," Ndesandjo said.
But even if their diverging views of the Obama family's history sometimes put the two siblings at odds, Ndesandjo said there were also things he was grateful for. His brother's example, he said, helped him re-embrace the Obama name that he had long shunned.
And some years ago, when they met after 20 years of separation, they shared some good times.
"We laughed, and we hugged, and that was one of the most wonderful moments of my life. And Barack made it possible," he said.
Ndesandjo, who lives near Hong Kong, hopes to raise awareness of domestic violence when the book is published in February. Some of the proceeds, he said, will go to his foundation for disadvantaged children.