SEOUL, South Korea — After the 14th-century Korean ruler Taejo, founder of the Joseon dynasty, chose the youngest of his eight sons to succeed him, a spurned son killed the heir apparent and at least one of his other half brothers and eventually rose to the throne. Today, rumors of royal fratricide are again swirling, this time around the court of Kim Jong-un, the ruler of North Korea.

Last week, Mr. Kim’s estranged older half brother, Kim Jong-nam, died in Malaysia, the apparent victim of a nerve-agent attack in the Kuala Lumpur airport. The Malaysian police named several suspects, including a North Korean diplomat. Many South Koreans, without needing proof, are calling it a political assassination directed by Kim Jong-un. North Korea denies that.

The Malaysian authorities may never be able to prove that Kim Jong-un was responsible for the death. But the rampant speculation that Mr. Kim ordered the attack is enough to send a chilling message to the North Korean people: Kim Jong-un’s reach and power can extend to all corners of the earth.

A head of state ordering a hit on his brother may sound medieval to modern ears. But in many ways, North Korea still operates like a feudal monarchy. The Korean tradition of leaders slaying their enemies and exiling potential claimants to the throne flourishes in Pyongyang.

Kim Jong-un’s father, Kim Jong-il, and grandfather both carried out deadly purges in the early years of their rule. And Kim Jong-il sent his half brother, Kim Pyong-il, to serve as ambassador to North Korea’s embassies in distant Poland and the Czech Republic.

Though he once appeared as the favorite to succeed his father, Kim Jong-nam began living abroad in exile after being caught in 2001 trying to enter Japan with a fake Dominican passport (the portly Mr. Kim used the name Pang Xiong, Chinese for “fat bear,” a detail that hints at his sense of humor).

The elder brother was better known for gambling than for politics. His young son, Kim Han-sol, affirmed that image in a 2012 interview in which he said, "My dad was definitely not really interested in politics.”

Still, Kim Jong-nam had been vocal in his criticism of the North Korean leadership. In 2010, as Kim Jong-un was being groomed to become leader, Kim Jong-nam told TV Asahi he opposed his father’s decision to pass leadership onto a third generation. And in a book published in Japan, Kim Jong-nam was quoted as predicting that North Korea would collapse without economic reform. These were damning words from a son of Kim Jong-il and could be cause for prosecution for treason under North Korean law.

The 2013 execution of Kim Jong-nam's uncle Jang Song-thaek was an omen. Mr. Jang, the husband of Kim Jong-il’s sister who at one time was treated as a regent for the young Kim Jong-un, was accused of plotting to overthrow the regime. His execution was meant to send North Koreans a message about the dangers of crossing Kim Jong-un and ushered in an extended purge. Kim Jong-nam was said to be close to his uncle.

The state media haven't mentioned Kim Jong-nam’s name in the reports on the death of a North Korean citizen in Malaysia, but word of the assassination has most likely circulated among elites. While Kim Jong-nam has not appeared much in the state media since falling out of favor with the regime more than 15 years ago, he was well known among elites and North Koreans who have spent time abroad — diplomats and, of course, defectors. These are the people who Kim Jong-un may have wanted to reach.

The death comes at a time when an unprecedented number of members of the North Korean elite are defecting to South Korea, most notably Thae Yong-ho, the dapper former deputy ambassador to Britain. Mr. Thae had been making the rounds divulging the inner workings of the Kim Jong-un regime, a blow to Pyongyang and a coup for Seoul.

As someone who traces her lineage to King Taejo, I have a personal interest in his long-ago palace drama. In 2013, I visited Taejo’s hometown, Hamhung, in North Korea, where locals shared details of the family legends.

The feuding among Taejo’s sons, I was told, so disheartened the king that he abandoned his palace in Seoul and retreated to Hamhung. For years, he refused to meet with the murderous son who eventually ascended to the throne. Legend has it that envoys bearing entreaties from the son, who ruled as King Taejong, were ordered slain before they could deliver their messages. The murdered envoys were called “Hamhung chasa” — messengers who never made it back home.

With his death, and all the speculation surrounding it, Kim Jong-nam has become a modern-day Hamhung chasa — a doomed man who never made it back home. And at least until we know more about the case, Kim Jong-nam’s demise will be seen as a warning to North Koreans of the fate they risk if they cross their leader.

This article originally appeared in the New York Times.