President Idriss Deby Itno of Chad was killed on Tuesday on the battlefield in fight against rebels, the military announced on national television.
Deby ruled the central African nation for more than three decades.
The military said Deby’s 37-year-old son, Mahamat Idriss Deby Itno, will lead an 18-month transitional council. The military also imposed a nightly curfew of 6 p.m.
Electoral officials had just declared Deby as the winner of the April 11 presidential election, giving him another six years in power, before he was killed on Tuesday.
Deby came to power in 1990 when his rebel troops overthrew President Hissene Habre. Deby was then the army commander-in-chief.
It was not clear exactly where and how the Chadian leader was killed. He has been battling Boko Haram terror groups and rebels opposing his rule. The army did not give enough information.
But Idriss Deby, who often joined the army on battlefield, had survived many rebellions against his rule.
The latest insurgency is led by a group calling itself the Front for Change and Concord in Chad. It was not clear whether it was that group that killed Deby.
The rebels are believed to have been trained in neighboring Libya and armed themselves there before crossing into northern Chad on April 11, the same day Deby was seeking a sixth term in office.