A mystery bidder paid $28 million at auction Saturday for a seat alongside Jeff Bezos on board the first crewed spaceflight of the billionaire's company Blue Origin next month. 

The Amazon founder revealed this week that both he and his brother Mark would take seats on board the company's New Shepard launch vehicle on July 20, to fly to the edge of space and back.

The Bezos brothers will be joined by the winner of Saturday's charity auction, whose identity remains unknown, and by a fourth, as yet unnamed space tourist.

Saturday's successful bidder beat out some 20 rivals in an auction launched on May 19 and wrapped up with a 10-minute, livecast frenzy.

The proceeds -- aside from a six percent auctioneer's commission -- will go to Blue Origin's foundation, Club for the Future, which aims to inspire future generations to pursue careers in STEM -- science, technology, engineering and mathematics.

Taking off from a desert in western Texas, the New Shepard trip will last 10 minutes, four of which passengers will spend above the Karman line that marks the recognized boundary between Earth's atmosphere and space.

After lift-off, the capsule separates from its booster, then spends four minutes at an altitude exceeding 100 kilometers, during which time those on board experience weightlessness and can observe the curvature of Earth.

The booster lands autonomously on a pad two miles from the launch site, and the capsule floats back to the surface with three large parachutes that slow it down to about a mile per hour when it lands.

Blue Origin's New Shepard has successfully carried out more than a dozen uncrewed test runs from its facility in Texas' Guadalupe Mountains.

The automated capsules with no pilot have six seats with horizontal backrests placed next to large portholes, in a futuristic cabin with swish lighting. Multiple cameras help immortalize the few minutes the space.