11:13 AM EST, February 4, 2014
He looks like President Obama, and even has a similar laugh.
Mark Obama Ndesandjo is the president's younger half-brother, but most people probably didn't know he existed.
Now, he's speaking exclusively to INSIDE EDITION, and what he says about his brother the president will surprise you.
Mark said, "He's very cold sometimes."
Intimate details about their tense relationship are revealed in Mark's just-released autobiography, Cultures: My Odyssey of Self-Discovery.
"My family's going to hate me for writing this book," said Mark.
And here's why—Mark and the president have the same father, Barack Obama Sr., and Mark's book paints a disturbing portrait of their dad as an abusive, violent alcoholic.
Mark told INSIDE EDITION, "I remember seeing my mother on the floor on one occasion with a knife to her throat."
Mark's mother, Ruth, a white, Jewish school teacher from Massachusetts married Barack Obama Sr. when they met at Harvard in 1964. Just a few months earlier, Barack Sr. had divorced the president-to-be's mom, Ann Dunham when he was only two years old.
Watch the full interview.
Young Barack grew up in Hawaii and never really knew his dad, while Mark was raised in Kenya and has painful memories.
"I'd always ask my mom to leave the door open, because kids are afraid of the dark. And there'd be the orange light coming from the living room and I remember the thuds and screams when my father came home. I also remember the scent of Johnny Walker Black Label."
Mark's mom finally left Barack Obama Sr. and later remarried. Mark took his Kenyan stepfather's last name and renounced his Obama heritage.
Mark was 22-years old when one day in 1988 the big brother he'd never met showed up unannounced at his home in Kenya. After that emotional first meeting, the Obama brothers lost contact for almost 20 years.
"I felt that my brother admired my father greatly, whereas I hated him," said Mark.
Mark graduated from prestigious Brown University, got a Masters from Stanford and an MBA from Emory University.
Now, here's a surprising twist—in 2002, he moved to Shenzhen, China, a bustling city of over 10 million near Hong Kong. He married a Chinese woman and learned to speak the language fluently.
He told INSIDE EDITION, "I decided to live in China because I was looking for a new life."
It was only during the 2008 presidential campaign that he decided to reconnect with his big brother. A never-before-seen home video shows the long-lost brothers reuniting for the first time in nearly two decades.
Mark caught the presidential candidate off guard when he flew from China to Austin, Texas, and showed up unannounced right before a debate with Hillary Clinton. His big brother looked surprised and uncomfortable. Some awkward chit-chat followed.
"It was amazing," recalled Mark. "We just laughed and we hugged each other and we were brothers."
Mark says he's not worried that his book could reopen old wounds with his long-lost brother.
"He said to me before he became a politician, 'Mark, go live your life and don't worry about me,' and that's what I'm doing," said Mark.