Kim Jong Il succumbed to a Heart Attack brought on by physical and mental exhaustion. In a "special broadcast" Monday from the North Korean capital, state media said Kim died of a heart ailment on a train due to a "great mental and physical strain" on Dec. 17 during a "high intensity field inspection." It said an autopsy was done on Dec. 18 and "fully confirmed" the diagnosis.

Kim is believed to have suffered a stroke in 2008, but he had appeared relatively vigorous in photos and video from recent trips to China and Russia and in numerous trips around the country carefully documented by state media. The communist country's "Dear Leader" _ reputed to have had a taste for cigars, cognac and gourmet cuisine was believed to have had diabetes and heart disease.

"It is the biggest loss for the party ... and it is our people and nation's biggest sadness," an anchorwoman clad in black Korean traditional dress said in a voice choked with tears. She said the nation must "change our sadness to strength and overcome our difficulties."

South Korean media, including Yonhap news agency, said South Korea put its military on "high alert" and President Lee Myung-bak convened a national security council meeting after the news of Kim's death. Officials couldn't immediately confirm the reports.

The news came as North Korea prepared for a hereditary succession. Kim Jong Il inherited power after his father, revered North Korean founder Kim Il Sung, died in 1994. In September 2010, Kim Jong Il unveiled his third son, the twenty-something Kim Jong Un, as his successor, putting him in high-ranking posts.

Traffic in the North Korean capital was moving as usual Monday, but people in the streets were in tears as they learned the news of Kim's death. A foreigner contacted at Pyongyang's Koryo Hotel said hotel staff were in tears.

As North Korea mourns, reaction to Kim Jong-il’s death has been coming in from around the world. US President Obama has spoken on the telephone to his counterpart in South Korea where the military is reportedly on alert. Lee Myung-bak has held emergency talks at home and called for calm, according to an official, asking residents to carry on with daily life.

In Seoul, company employee Oh Eun-mi, 30, expressed fears for the impact on the South’s market and economy. People were always concerned about Kim Jong-il’s death, she said, predicting a negative effect initially but a positive outcome in the long-term. “I think there will be some kind of provocation from North Korea, to strengthen domestic unity,” said fellow Seoul worker Choi Hwa, 28. “But I am not worried about it. It will just be a strategy. And we do have the military power.”

From Chinese condolences to the US restating its commitment to stability on the Korean peninsula, Kim Jong-il’s death has had a truly global impact.