A soon-to-be released tell-all rips the lid off the secret war between Barack Obama and his half-brother – who denounced the President as “a stuck-up a**hole.”

In his autobiography, Mark Obama Ndesandjo accuses his brother of being a cold-hearted academic who couldn’t care less about the abusive behavior of their alcoholic father, Barack Obama Sr.

Barack is reportedly upset over the scathing book – scheduled for release Sept. 16 – which also highlights alleged factual errors in the Commander-in-Chief’s 1995 memoir “Dreams from My Father.”

While Obama Sr. abandoned young Barack and his mother, his brother caught the full brunt of the old man’s cruelty.

“Every blow my father gave my mother, I felt,” says Mark, “and each time it seemed to shatter the safe world I was trying to 
construct for myself.”

The friction between Barack and Mark burst into the open in 1988 when Harvard-bound Barack visited his Stanford-bound half-brother in Kenya to explore his African roots and inquire about his father, who had wed Mark’s mother after divorcing Barack’s mom, Ann Dunham.

While at an Indian restaurant in Nairobi, Barack used his smooth-talking legal skills to get Mark to spill about their father.

“Do you even know what your father did to us?” Mark blurted out during the interrogation.

“I don’t know and I really don’t care,” the future President coldly replied.

But those years still resonate loudly for Mark. In his book, he tells of waking up in the middle of the night in Kenya: “When I was abruptly woken up, I would see light streaming in around the sides of the door. There would be thumps and yells, often followed by the sound of my mother screaming in pain or anger.”

For years, Mark used only his stepfather’s surname to forget his cruel biological father. Early on, Mark abandoned his African roots while a youthful Barack, who grew up with a white mother, sought to connect with it by learning about his absent father. Obama Sr. died in 1982 at age 46 in a car crash.

Of the restaurant confrontation, Mark says, “This man sitting across the table from me was my brother granted. But We had barely met and now he was exploring my darkest past, asking me those intensely personal questions…Barack was relentless in his questioning. What a stuck-up a**hole.

“His demeanor was cold,” he recalls. “I felt he was an arrogant bastard but was too polite to say so to his face. I did not enjoy being treated as a research subject.”

The two men met again and reconciled during a 2008 presidential campaign stop in Austin, Texas, where Mark gave his half-brother a Chinese calligraphy that read, “So close, yet so far. So far, yet so near.”

But that friendly gesture did not stop Mark from using his book’s appendix to painstakingly point out what he believes are factual errors in the President’s celebrated book, “Dreams from My Father.”

Mark writes: “Here I have detailed some points in it that need to be finally corrected, as they have led to years of rumors and false assumptions about family relationships, which, in some cases, have hurt people.”

He takes aim at a portion 
of “Dreams” in which Barack’s half-sister is quoted as saying that Mark’s mother, Ruth Baker, encouraged her sons to avoid contacting the Obama family after she remarried.

He counters, “My mother never discouraged me from contacting the Obamas. It was my decision not to do so.”

Mark, who earned degrees in physics from Brown and Stanford Universities, lives with his wife in China, where he is an author, pianist and brush calligrapher.