Frank McCourt, the author of bestseller Angela's Ashes, is battling the deadly skin cancer melanoma and may have only weeks to live.
The Pulitzer Prize winner, who is due to celebrate his 79th birthday next month, was transferred to a hospice at the weekend.
According to the writer's brother Malachy McCourt, who spoke publicly about his brother's illness in May, the cancer was then in remission following a course of chemotherapy.
Describing his brother as “a hearty fellow” who had survived worse, Mr McCourt, an actor and author, denied several media reports that his brother was on his deathbed.
After receiving treatment at the world-famous Memorial Sloan Kettering hospital in New York, the writer was declared well enough to return home to Connecticut.
However, a friend said yesterday that Mr McCourt's condition has deteriorated dramatically since then and that he is seriously ill.
It is understood he became unwell while on a cruise in the Pacific and was transferred to a hospital in Tahiti.
The Brooklyn-born former schoolteacher shot to fame relatively late in life with the publication of ‘Angela's Ashes' in 1996, when he was 56 years of age.
The memoir tells the tale of his impoverished childhood in Limerick after his alcoholic father Malachy and his mother Angela moved back there when he was just four years old. The book won the Pulitzer Prize in 1997.
His second book, ‘’Tis', picked up the story of his life where Angela's Ashes left off, with his arrival in America at age 19.
His 2005 memoir, ‘Teacher Man', chronicled his 27-year career in the New York City school system.
Both books were instant bestsellers.
For 30 years, Mr McCourt taught in New York City high schools, having earned a degree at New York University.
He recently made his first venture into children's books with ‘Angela and the Baby Jesus', based on an incident from the childhood of his mother Angela. In an interview at the end of 2007 he said that he was in the middle of writing his first novel, and was also planning a book for teenagers.