Tory Burch, the fashion designer who popularized $200 ballet flats, is officially a billionaire.

The 46-year-old designer added nine zeros to her net worth following the sale of part of her ex-husband's stake in her company, Tory Burch LLC, Bloomberg reported. The sale valued the company at nearly $3.3 billion and gave Burch a 28.3 percent stake in the high-end clothing and accessory brand.

Burch's ex-husband Chris Burch retains a 15 percent share in the company, according to Bloomberg.

The sale now makes Burch the second youngest self-made female billionaire in America, according to Forbes. The youngest is Spanx inventor Sara Blakely, who made Forbes' billionaire list in 2012 at age 41.

The designer's rise to billionaire status has been rapid. In 2004, with her then-husband Chris, Burch opened her first store in New York City. Today the brand has more than 80 retail locations and is sold in high-end retailers such as Neiman Marcus. The brand is best know for its colorful ballet flats that are emblazoned with its signature double-T logo and cost upward of $200 per pair.

The secret to her success? Sources have called Burch "punctual, efficient, and focused to a fault" according to a December story in Vanity Fair. She also had a wealthy upbringing: Her father was heir to a paper-cup fortune.

Other American fashion billionaires include Ralph Lauren, who is worth $7.5 billion. Designer Michael Kors has been on the billionaire-watch list for the past year and is worth around $780 million, according to Forbes. Kate Spade, a designer whose namesake brand is often compared to Tory Burch, sold her luxury patrician-chic brand to Liz Claiborne in 2006 for $124 million and is worth an estimated $150 million.

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