The announcement came just a month after the man known as the "Kaiser" for his dominance of the industry did not appear at his Paris haute couture week show for Chanel, which he led since 1983.
Friends have always said that the prolific creator would die with a pencil in his hand, and just last week his own fashion line Karl Lagerfeld was still announcing new design collaborations.
German-born Lagerfeld was artistic director of three separate brands at the same time right up to his death: France's Chanel -- the world's richest label -- Italy's Fendi and his eponymous line.
Bernard Arnault, owner of the luxury giant LVMH -- the most powerful man in fashion -- said he was "infinitely saddened" by the loss of a "very dear friend" and a "creative genius".
"Fashion and culture have lost a major inspiration. He contributed to making Paris the fashion capital of the world and Fendi one of the most innovative of Italian brands," the billionaire said.
With his powdered white pony tail, black sunglasses and starched high-collared white shirts, Lagerfeld was as instantly recognisable as his celebrity clients.
News of his death led to an outpouring of emotion in the industry, and tributes began flowing in from politicians and fans.
"It's a privilege to be able to say that you've worked with him, that you've listened to him speak, that you've talked with him, that you've been dressed by him," said the French actress and singer Vanessa Paradis on Instagram.
"Karl Lagerfeld is an immense personality, someone out of the ordinary," French Interior Minister Christophe Castaner told RTL radio.