Abdelbaset Ali Mohmet al-Megrahi, the Libyan convicted of the 1988 Lockerbie plane bombing, returned home on Monday to be with his family, his brother told AFP, with no prospect of recovery.
"He is still very very sick, in the final stages of a cancer which has no cure, so his days are numbered," said his brother Abdelhakim al-Megrahi, adding that he had brought his sibling home from the hospital in the afternoon.
Megrahi spent three days in hospital where he received a blood transfusion.
"No one can say whether he will live or die -- only God knows," he added.
Abdelhakim defended his brother, who suffers from prostate cancer, saying he was "exploited" by the regime of Moamer Kadhafi who let him take the blame for a crime he did not commit.
A Scottish court in 2001 convicted Megrahi of the December 1988 bombing that killed 270 people, but he was released on compassionate grounds in 2009 and allowed to return to Libya.
Doctors said at the time that he had terminal cancer and only three months left to live.
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Last August, during the revolution which toppled Moamer Kadhafi, another of of Megrahi's brothers told reporters outside the family home in Tripoli that he was "in and out of a coma."
Amid the lack of law and order after the revolt which brought armed fighters out onto the streets, his medicine had been looted and no doctors were available, the family said.
Megrahi had been greeted as a hero on his return to Kadhafi's Libya, after having served eight years of a minimum 27-year sentence for his role in the bombing of Pan Am Flight 103.
The fact that he has survived so long has provoked indignation in Britain and the United States.
On the second anniversary of the release of the former Libyan intelligence agent who has always maintained his innocence, the Scottish government insisted its decision to free him had been vindicated.
But British Prime Minister David Cameron has criticised the release as a "terrible mistake," and Deputy Prime Minister Nick Clegg said he would like to see him "back in jail behind bars."
Most of those killed in the bombing of the Boeing 747 jet headed from London to New York were Americans. All 259 passengers and crew were killed, along with 11 people on the ground.