Oprah Winfrey once famously said: "It was never about attaining wealth or celebrity" — but the talk show queen has managed to amass plenty of both.

The showbiz legend has just been named as the first female black entrepreneur to make it onto the Bloomberg Billionaires Index, taking out the 486th spot thanks to her incredible $US4.04 billion fortune.

Talk show host Oprah Winfrey holds her Daytime Emmy for Outstanding Talk or Service Show Host, awarded for the Oprah Winfrey Show, 1987. Photo / Getty
Talk show host Oprah Winfrey holds her Daytime Emmy for Outstanding Talk or Service Show Host, awarded for the Oprah Winfrey Show, 1987. Photo / Getty

While the bulk of the self-made 64-year-old's wealth comes from the show that made her a global household name, The Oprah Winfrey Show, it turns out a huge chunk of her riches also come from another, more surprising source.

In 2015, the actor and former talk show host bought a $58.6 million, 10 per cent stake in weight loss company Weight Watchers, snapping up around 6.4 million shares at $A9.22 apiece.

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The value of the Weight Watchers shares more than doubled soon after the partnership was announced, and since 2015, the value of the company has continued to explode.

Today, it's worth a whopping $A140.03 a share — an increase that has increased Winfrey's personal fortune by more than half a billion dollars.

Oprah Winfrey speaks onstage during the 45th NAACP Image Awards presented by TV One at Pasadena Civic Auditorium on February 22, 2014 in Pasadena, California. Photo / Getty
Oprah Winfrey speaks onstage during the 45th NAACP Image Awards presented by TV One at Pasadena Civic Auditorium on February 22, 2014 in Pasadena, California. Photo / Getty

Since becoming a partial owner of the US company, Winfrey went on the weight loss program herself, and lost 20kg — becoming a walking advertisement for the brand in the process.

"Weight Watchers has given me the tools to begin to make the lasting shift that I and so many of us who are struggling with weight have longed for," Winfrey said in a statement at the time the deal was signed.

"I believe in the program so much I decided to invest in the company and partner in its evolution."