Mexican drug lord Hector Beltran Leyva, a onetime associate of Joaquin "El Chapo" Guzman, who has been in a maximum security prison since 2014, died Sunday of a heart attack, officials said.
With his brothers Alfredo, Arturo and Carlos, Mr Leyva was part of Guzman's powerful cartel in Sinaloa until they separated in 2008 and launched their Beltran Leyva cartel. Mr Guzman is currently on trial in New York.
"Inmate Hector Manuel Beltran Leyva, known by the alias of 'H,' died in a Toluca hospital after a heart attack," an official statement said.
Prior to his arrest in October 2014 at a seafood restaurant in San Miguel de Allende, Mr Leyva was the last of the four brothers to head the cartel.
Brought to the US almost 22 months ago, Mr Guzman, 61, is accused of smuggling more than 155 tons of cocaine into the United States over 25 years and faces life in prison if found guilty.
His lawyers argue he has been scapegoated by Mexico's "corrupt" government and the US Drug Enforcement Agency, and that the cartel's true chief was Ismael Zambada.