NEW YORK — Princess Marcella Borghese, founder of the cosmetics line that bears her name, died of natural causes at her home in the Swiss town of Montreux over the weekend, according to friends.

Details of her death and her age could not be learned; she was believed to be 93.

The princess, who was also the Duchess of Bomarzo, was living in retirement following the passing of her husband, Prince Paolo Borghese, Duke of Bomarzo and former president of General Motors in Italy.

Under the business guidance of Revlon founder Charles Revson, the princess launched Princess Marcella Borghese Inc. in 1957. The firm became a wholly owned subsidiary of Revlon, whose interest in marketing an upscale brand made the union a mutually attractive deal.

After focusing on charity work for orphans in Italy after World War II, the princess turned her attention to developing a cosmetics line. With inspiration, glamour and personality on her side, she met Revson through social connections and realized the potential of launching a line with the expertise of beauty executives.

During the late Eighties, the Princess Marcella Borghese line impacted the spa treatment category when it launched Terme di Montecatini, a line that uses fango mud and moisturizers made with waters from Montecatini.

Revlon later sold its Princess Marcella Borghese and Halston divisions to Saudi investors and in 1991, the two units were combined, becoming HalstonBorghese. Following a breakup of that firm, the name of the brand was shortened to Borghese in 1997.

Dan Moriarty, a long-time associate of the princess at Revlon, pointed to her enduring devotion to her brand. He cited the princess’s appearances at events that featured models covered head-to-toe in mud.

“She was always exuberant about her cosmetics business and loved the whole life,” Moriarty remarked. “She was committed to it always, out there very visibly participating until she was 80. She was the type who maintained long-term personal relationships with the Marcuses of Neiman Marcus, Harrod’s, Saks — top stores all over the world.”

The princess and Paolo moved from Italy to Chalet Roa in Carns-Sur-Fierre, Switzerland, during the late Seventies. They lived there together until after Paolo’s death in the late Eighties.

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The princess is survived by her twin sons, Livio, who assumed his late father’s title, and Francesco, a retired cosmetics executive living in New Jersey. Both are married and have children of their own.