The brother of Gabriel Garcia Marquez says that the Colombian writer and winner of the 1982 Nobel Prize for Literature is suffering from dementia.
Jaime Garcia Marquez told students at a lecture in the city of Cartagena that his brother, who is 85, phones him frequently to ask basic questions.
"He has problems with his memory. Sometimes I cry because I feel like I'm losing him," he said.
He says the author has stopped writing altogether.
The BBC's Arturo Wallace in Colombia said there have been rumours about Mr Garcia Marquez' memory problems.
Jaime Garcia Marquez, his younger brother, is the first family member to speak publicly about it.
Invited to talk about his relationship with Gabo, as the writer is affectionately known in Colombia, Jaime said he could not hold back from talking about his illness anymore.
"He is doing well physically, but he has been suffering from dementia for a long time," he said. "He still has the humour, joy and enthusiasm that he has always had."
The 1967 masterpiece of magic realism, One Hundred Years of Solitude, begins with the story of a family unable to care for their senile grandfather.
"It is a disease that runs in the family," said Jaime Garcia Marquez.
Gabriel Garcia Marquez currently lives in Mexico and has not made many public appearances in recent years.
His novels include Love in the Time of Cholera, Chronicle of a Death Foretold and the The General in His Labyrinth.
He is best known for One Hundred Years of Solitude, which has sold more than 30 million copies and been translated into more than 30 languages .