Updated at 3 p.m. ET

The half-brother of North Korean leader Kim Jong Un has reportedly died in Malaysia under suspicious circumstances, according to multiple media outlets. Kim Jong Nam is also the eldest son of former leader Kim Jong Il.

Neither the Malaysian nor the North Korean governments have officially confirmed the death of the man who was once thought to be Kim Jong Il's successor. NPR has not independently confirmed the reports.

In a statement provided by NPR's Elise Hu in Seoul, Malaysian police said they are investigating the suspicious death of a North Korean man who became ill at the Kuala Lumpur International Airport on Monday, then died on the way to the hospital.

The police identified the deceased man as 46-year-old "Kim Chol," and said that an "investigation is in progress and a post mortem examination request has been made, to ascertain the cause of death."

It was not immediately apparent whether Kim Chol was a pseudonym used by Kim Jong Nam. Journalist Jean Lee, a global fellow at the Wilson Center, tells All Things Considered that "Kim Chol" is a very common name in North Korea. "So it would be like 'John Smith' ... a name that would be easy to sort of fly under if you're going to use a pseudonym."

The circumstances of the man's death are mysterious. The Associated Press cited a Malaysian official as saying that the man told medical workers he was attacked with a chemical spray. But South Korean media reports allege that two women attacked the man with a needle. Again, NPR has not independently verified this information.

Kim Jong Un, the third-eldest known son of Kim Jong Il, emerged as the heir-apparent in 2009. There are still questions about exactly how that happened — as NPR has reported, he was seen as an unlikely successor. But we do know that Kim Jong Nam fell out of favor with his father in 2001 when he was caught trying to travel to Japan to visit Disneyland using a fake passport from the Dominican Republic.

Kim Jong Nam has been described as a "playboy" and also reportedly told Japanese broadcaster Asahi in 2011 that he had reservations about North Korea's hereditary transfer of power.

Lee says Kim Jong Nam is believed to have feared for his life, and described his relationship with Kim Jong Un:

"They have different mothers, and he is the older half-brother. They did not grow up together, and they did not, clearly, have a close relationship. One of the things that Kim Jong Nam may have been worried about is that Kim Jong Un in 2013 ordered the execution of his own uncle. So one thing we learned about then was Kim Jong Un would spare no one, not even a family member, who had crossed him or had crossed the regime."

In recent years, Lee says, Kim Jong Nam has spent most of his time outside of North Korea, primarily in the Chinese territory of Macau, where he was believed to live a "flamboyant lifestyle."

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