(Bloomberg) — Amazon.com Inc. Chief Executive Officer Jeff Bezos sold about $1 billion in company stock as part of a planned divestiture, a month after the world’s third-richest man said he spends about that amount annually on his space exploration company Blue Origin LLC.

Bezos sold 1 million shares from Tuesday to Thursday ranging in price from about $935 to $950 per share, according to a regulatory filing on Thursday.

He still owns 79.9 million shares, or about 17 percent of the company, down from 83 million shares at the end of 2015.

Amazon’s growing e-commerce business and profitable cloud-computing division has propelled its founding CEO up the ranks of the world’s wealthiest people, where he is now No. 3 behind Microsoft co-founder Bill Gates and Spanish entrepreneur Amancio Ortega Gaona, according to the Bloomberg Billionaires Index.

Bezos has been selling Amazon stock to invest in Blue Origin, which aims to send tourists on brief flights into suborbital space where they can experience weightlessness and get a nice view of the Earth.

His competitors in space tourism include Elon Musk’s Space Exploration Technologies Corp., which hopes to send tourists around the moon next year, and Richard Branson’s Virgin Galactic.