The founder of the controversial extremist Westboro Baptist Church, Fred Phelps, is "on the edge of death" at the Midland Hospice in Topeka.
The announcement was made by his son Nathan Phelps, on Facebook on Sunday.
Nathan Phelps, the sixth of Fred Phelps' thirteen children, left the WBC over three decades ago, and has since become a campaigner for LGBT causes.
He described himself as being "bitterly angery" that he and other family members were not being allowed to say their goodbyes to their father.
He also revealed that his father had been excommunicated by the WBC in August 2013, although the reasons for this remain unclear.
"I'm not sure how I feel about this," Nathan Phelps said.
"Terribly ironic that his devotion to his god ends this way. Destroyed by the monster he made."
He added: "I feel sad for all the hurt he's caused so many. I feel sad for those who will lose the grandfather and father they loved."
Fred Phelps was a Kansas based lawyer who became associate pastor of East Side Baptist Church in Topeka in 1954. He was asked to be the lead pastor on a new Baptist church they set up in Westboro in 1955.
Shortly after that, Fred Phelps severed all ties with East Side Baptist Church.
He was later disbarred in 1979 for verbally abusing a witness in a case, accusing her of obscene sexual acts and causing her to cry during her cross-examination. He was ultimately found guilty of making false statements in court.
He and the WBC gained local notoriety in 1991 when they began protesting Topeka's Gage Park, alleging that it was a hub for public homosexual activity in the area.
Later, their protests went nationwide. In 1994 Fred Phelps claimed that the overwhelmingly negative public reactions to the protests were proof of their righteousness.
They are particularly reviled for regularly picketing the private moments of grieving families of fallen military personnel. The WBC claim that the death of American soldiers is God's judgement on a country tolerant of homosexual activity.
Their placards usually include homophobic and anti-Semitic phrases such as "God hates fags", "Thank God for dead soldiers", "God hates Israel", "The Jews killed Jesus", and "God: USA's terrorist".
The WBC have protested at the Ground Zero site on the 10th anniversary of the 9/11 attacks in New York, and have been banned from entering the UK to protest a school play.
In July 2013, they picketed a One Direction concert in Kansas City, Missouri, where they described the band as "crotch-grabbing little perverts" according to the Independent.
A 2011 Louis Theroux documentary on the WBC entitled 'America's Most Hated Family in Crisis' found that many of the younger members of the less than 100 strong cult were choosing to leave, putting the organisation's future in doubt.
The WBC have been unwilling to comment directly on the health situation of Fred Phelps, only admitting that he was receiving hospice care.
WBC spokesman Steve Drain told the Topeka Capital-Journal that: "We don't owe any talk to you about that. We don't discuss our internal church dealings with anybody. It's only because of his notoriety that you are asking."