Veteran politician John Keen died aged 90, on Christmas Day, at Aga Khan Hospital in Nairobi where he was being treated.
Keen's son Anthony told the Star that he was admitted on Wednesday and that funeral arrangements will be announced soon.
Other family members said he had been sick for a while but was able to manage his properties in Karen and Namanga, where he has more than 1,500 camels and cattle.
Keen once served as assistant minister during the reign of former President Daniel Moi in the 1980s.
The Maasai politician served as Kajiado North MP from 1969 to 1979 under Kanu before falling out with Moi over the majimbo issue.
He later joined retired President Mwai Kibaki and formed the Democratic Party which he served as Ssecretary General.
Keen was recently in the news when the High Court rejected an attempt to subject him to a DNA test in a paternity case.
High Court judge Mumbi Ngugi ruled that Ruby Kimani, 35, did not establish any biological relations with Keen.
Kajiado South MP Katoo ole Metito was first to break the news of Keen’s demise. He said the cruel hand of death had snatched his close friend and political mentor.
Others who sent condolence messages included former assistant minister David Sankori, Kajiado politician Oliver Seki and Governor David Nkedianye
"I have received news of the death... with profound shock and regret," Deputy President William Ruto posted on Twitter.
"The ODM family mourns John Keen; one of the true founders of our nation. With men like Keen, democracy flourished here for a time," the party wrote on Twitter.