Blackwell, 85, is best known for his annual best and worst dressed lists, but he also worked as an actor, Hollywood agent and costume designer during his storied career.
His longtime companion and business partner, Robert Spencer, told the Newark (N.J.) Star-Ledger Thursday that Blackwell has been hospitalized with a serious illness.
Although Spencer declined to discuss the nature of the fashion maven's illness or where he is being treated, Spencer did say Blackwell has been unconscious since Tuesday.
Notable deaths of 2014 [PHOTOS]
Mindy Kaling mistaken for Malala Yousafzai