MacKenzie Bezos became world's 3rd richest woman, acquiring a 4% stake in Amazon worth about $36 billion

MacKenzie Bezos, the former wife of Amazon.com Inc Chief Executive Officer Jeff Bezos, pledged on Tuesday to give half of her $36 billion fortune to charity, following a movement founded by billionaires Warren Buffett and Bill and Melinda Gates.

Bezos, whose former husband is the world's richest man, was one of 19 people on Tuesday to join the "Giving Pledge," a campaign announced in 2010 by Berkshire Hathaway Inc's Buffett and Microsoft Corp co-founder Bill Gates. It calls for the super-rich to give away more than half their fortunes during their lifetimes or in their wills.

"In addition to whatever assets life has nurtured in me, I have a disproportionate amount of money to share," MacKenzie Bezos said in a statement dated Saturday. "My approach to philanthropy will continue to be thoughtful. It will take time and effort and care."

MacKenzie Bezos became the world's third-richest woman, according a Forbes Magazine, acquiring a 4% stake in Amazon worth about $36 billion when she and Jeff Bezos announced their divorce settlement on April 4.

Jeff Bezos, whose net worth was estimated by Forbes at $131 billion this year, was quick to support his ex-wife's new philanthropic endeavor.

"MacKenzie is going to be amazing and thoughtful and effective at philanthropy, and I'm proud of her," he said on Twitter. "Her letter is so beautiful. Go get 'em MacKenzie."

Jeff Bezos, who tops the Forbes list of world billionaires, is not among the 204 wealthy "Giving Pledge" signatories from 23 countries who come from a wide range of fields, including finance, technology, healthcare and real estate development.

Other Forbes top 10 billionaires who have not joined the "Giving Pledge" are Bernard Arnault, head of French luxury goods conglomerate LVMH; Mexican telecommunications magnate Carlos Slim; European fashion retail mogul Amancio Ortega and Google co-founder and Alphabet CEO Larry Page.

The pledge that signatories make is "a moral commitment to give, not a legal contract," the campaign said on its website.