Colombian government officials say they have confirmed the death of Manuel Marulanda - the commander of the Revolutionary Armed Forces or FARC.
Rumors about the aging rebel's death or serious illness have surfaced before, but were never confirmed.
Government officials did not reveal how they were able to verify the rebel leader's death.
The announcement followed the publication Saturday of an interview with Colombia's defense minister, who told Semana magazine that Marulanda was probably dead. Santos said a reliable contact told him Marulanda died of a heart attack.
Marulanda - also known as "Sureshot" - led the leftist FARC insurgency for more than 40 years.
Colombia, the United States and the European Union label the FARC a terrorist group.
Some information for this report provided by AP and Reuters.