Kim Jong Un's half-brother, who was reportedly assassinated by the North Korean regime, was a CIA source who met with the U.S. spy agency's officials on several occasions, according to a new book.

President Donald Trump said Tuesday that he would not allow that to happen, extending another olive branch to the North Korean leader as his diplomatic push to dismantle the regime's nuclear weapons program has stalled.

"That would not happen under my auspices," Trump said. "That's for sure."

Kim Jong Nam was killed in Kuala Lumpur International Airport in Malaysia in February 2017 by two women who poisoned him with the nerve agent VX. While North Korea has denied any involvement, U.S. and South Korean officials say the highly secretive country was responsible.

Kim Jong Nam's possible ties to the CIA were first reported in the new book "The Great Successor" by Washington Post reporter Anna Fifield. ABC News has not independently confirmed the claim. The CIA declined to comment.

While it may not be surprising that the CIA would want to speak with Kim Jong Un's half-brother, according to several analysts and former U.S. officials, it also is debatable how much information he would have to share, given that he lived outside the country for approximately 15 years before he was murdered.

"It would not be surprising if Kim Jong Nam had been meeting with the CIA, offering any insights into what he knew of the inner workings the Kim regime and trends among Pyongyang elites. However, given his exiled status, it’s hard to say how accurate those insights may have been," said Jenny Town, managing editor of 38 North, which analyzes North Korea.

But given how little the U.S. knew about Kim Jong Un when he succeeded his father and came to power in 2011, any insights into who he is and what he is like would have been valuable, according to some former officials.

"Picture Kim Jong Un as the bullseye with family, friends and associates being the concentric rings going outward. Kim Jong Nam likely had enough personal, intimate, and family information in his head to warrant an approach from CIA -- or any intelligence agency -- for debriefing purposes," said Darrell M. Blocker, a longtime CIA operative and now an ABC News contributor.

It's unclear when Kim Jong Nam first met with CIA officials or how often. Based in the Chinese enclave Macau, he was the oldest son of Kim Jong Il and was thought to be the heir apparent until he went into exile in the early 2000's.

Despite that exile, there has long been speculation that foreign intelligence agencies -- especially China's -- maintained contact with him, in particular, as a possible leader in case Kim Jong Un fell from power. That potential threat to Kim Jong Un's power was likely motivation for the assassination plot against Kim Jong Nam.

Kim Jong Un "has not been shy about purging, demoting, shuffling senior officials -- numbering in the hundreds since he came to power in December 2011 -- and instilling fear in the North Korean populace, but also among the elite who rely on his good will for their survival," said Jung Pak, a senior fellow at the Brookings Institution, who added that because of his brother's tight control of power, Kim Jong Nam -- like most North Koreans who live outside the country -- probably have little "access to the innermost workings of the Kim regime, much less on decision-making on the most sensitive issues, such as the nuclear weapons program."

Kim Jong Nam was in Malaysia that February 2017 when he was killed, reportedly in part to meet his CIA contact, according to the Wall Street Journal.

During the trial of the two women who conducted the assassination, police said he spent several days at a resort on Langkawi, a Malaysian island, where he met with an unknown Korean-American man. Malaysia has released both of the women -- Doan Thi Huong of Vietnam and Siti Aisyah of Indonesia, who said that they believed they were participating in a TV prank show.