Obama, who spent three days in China during his first official tour of Asia, acknowledged the meeting in an interview with CNN. He offered no details. An aide said later that the meeting took place Monday night after Obama arrived in Beijing, the Chinese capital.
The White House had declined to say whether the president and Mark Ndesandjo would meet. And no White House official mentioned the visit until Obama did when asked about it.
"I don't know him well. I met him for the first time a couple of years ago," Obama told CNN. "He stopped by with his wife for about five minutes during the trip."
Describing the meeting as "overwhelming" and "intense," Ndesandjo told The Associated Press in an interview Wednesday that he had long anticipated the chance to welcome his famous brother to China.
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"I think he came directly off the plane, changed some clothes and then came down and saw us," Ndesandjo told AP Television News on Wednesday. "And he just gave me a big hug. And it was so intense. I'm still over the moon on it. I am over the moon. And my wife. She is his biggest fan and I think she is still recovering."
In the CNN interview, Obama said he hadn't read his brother's book, "Nairobi to Shenzhen," in which Ndesandjo says Barack Obama Sr. beat him and his mother. The president also wrote about his father, who had abandoned him as a child, in his best-selling memoir, "Dreams from My Father."
"It's no secret that my father was a troubled person," Obama said. "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. Obviously it's a sad part of my history and my background but it's not something I spend a lot of time brooding over."
Ndesandjo said he bought tickets months ago to fly to from the southern boomtown of Shenzhen, where he has lived since 2002, to Beijing, in hopes of reconnecting with his brother. The two last met in January when Ndesandjo attended Obama's inauguration as a family guest.
The three chatted, with Obama being introduced to Ndesandjo's wife, a native of Henan, China, whom he married a year ago, he said. He gave few details of what they discussed.
"All I can say is, we talked about family, and it was very powerful because when he came in through that door, and I saw him and I hugged him, and he hugged me and hugged my wife. It was like we were continuing a conversation that had started many years ago," he said.
The two men did not grow up together. Ndesandjo's mother, Ruth Nidesand, was Barack Obama Sr.'s third wife. Before arriving in Beijing on Monday, Obama had been in a townhall-style meeting with students in Shanghai, and joked that a family gathering at his house "looks like the United Nations."
President Obama's father had been a Kenyan exchange student who met his mother, Kansas native Stanley Ann Dunham, when they were in school in Hawaii. The two separated two years after he was born.
The senior Obama married Ndesandjo's mother after divorcing the president's mother. They returned to Kenya to live, where Mark and his brother, David, were born and raised.
Obama Sr. died in an automobile accident in 1982 at age 46.
Ndesandjo lives near Hong Kong and earns a living as a marketing consultant. For most of that time, he has maintained a low profile, with few people knowing of his connection to the U.S. president.