MacKenzie Bezos on Tuesday pledged to give away at least half of her $36 billion fortune to charity.

Bezos became the world's third richest woman, according to Forbes, following her divorce from Amazon founder Jeff Bezos earlier this year.

MacKenzie Bezos was one of 19 on Tuesday to join the 'Giving Pledge' - a campaign founded by Bill and Melinda Gates and Warren Buffett encouraging the mega-rich to give away 50 percent or more of their wealth.

In a letter, Bezos said "My approach to philanthropy will continue to be thoughtful.

It will take time and effort and care.

But I won't wait." In a tweet, Jeff Bezos praised the move saying "MacKenzie is going to be amazing and thoughtful and effective at philanthropy, and I'm proud of her.

Her letter is so beautiful.

Go get 'em MacKenzie." While many on the Forbe's list of richest people have signed onto the pledge, Jeff Bezos, who tops the list, has not.