Brunello Cucinelli, the 59-year-old founder of the luxury fashion house that bears his name, has become a billionaire.

Knitwear brand Brunello Cucinelli SpA has more than doubled in value since its initial public offering in Milan last April, giving Cucinelli a net worth of at least $1 billion, according to the Bloomberg Billionaires Index. He has never appeared on an international wealth ranking.

“From the beginning we hoped for a positive and gentle listing,” Cucinelli said by phone from his Milan showroom through a translator. “Investors appreciate our quality, our positioning in the absolute luxury market and our Italian heritage.”

The Solomeo, Italy-based company, which sells $4,530 suede jackets and $1,920 cashmere cardigans, had sales of $360 million in 2012, up 15.6 percent in a year. It forecast “modest double- digit” revenue growth for 2013, Bloomberg News reported in February.

“It is chic sportswear where the quality of the finishing is very high,” Armando Branchini, founder of Milan-based luxury consultant Intercorporate, said in a telephone interview. “Cucinelli offers couture finishing, elegance and sophistication and yet you can wear it in a very casual way.”

Cucinelli’s 63 percent stake is valued at $947 million. He collected more than $90 million selling shares in the IPO. Company shares rose four cents to 16.75 euros in Milan trading today, giving it a market capitalization of $1.5 billion.

Fashion Fortunes

“I am thankful, but in all honesty, my life has remained the same as when I was working alongside my father, farming in the countryside,” Cucinelli said, without commenting specifically on his net worth. “The most important thing is that we managed to achieve this success while respecting our workers, the people of Solomeo and the environment.”

Cucinelli joins new fashion billionaires such as Tory and Chris Burch, as well as Alberto Prada Bianchi and Marina Prada Bianchi, all of whom have benefited from a booming luxury market and the resulting surge in values of fashion retail companies.

The Bloomberg European Luxury Goods Index, whose nine constituents include London-based Burberry Group Plc and Germany’s Hugo Boss AG, has risen 13.3 percent in 2013. In its annual luxury market report in October, Boston-based consultancy Bain & Co. said global sales of apparel, accessories, cosmetics and fragrances would expand by 10 percent in 2012 to $270 billion, and estimated growth of four to six percent per year between 2013 and 2015.