A mystery bidder spent US$28 million at auction on Saturday for a seat alongside Jeff Bezos on the billionaire's business Blue Origin's first crewed mission, which will take place next month.

Last week, the Amazon founder said that he and his brother Mark would fly to the edge of space and back aboard the company's New Shepard launch vehicle on July 20.

The Bezos brothers will be accompanied by the winner of Saturday's charity auction, whose identity has yet to be revealed, as well as a fourth, unannounced space tourist.

Following the sale, Blue Origin tweeted, "The name of the auction winner will be published in the weeks following the auction's conclusion."

"After that, the fourth and final member of the crew will be revealed - keep tuned."

In an auction that began on May 19 and ended with a 10-minute livecast frenzy on Saturday, the winning bidder beat out more than 20 competitors.

By Thursday, bidding had reached US$4.8 million, but it soared in the last live auction, climbing in million-dollar increments.

Aside from a 6% auctioneer's charge, all revenues will go to Blue Origin's Club for the Future charity, which strives to inspire future generations to pursue careers in STEM (science, technology, engineering, and mathematics).

The New Shepard flight will take off from a desert in western Texas and last 10 minutes, with four passengers.

The capsule separates from its launcher after lift-off and spends four minutes at an altitude of more than 100 kilometers, during which time passengers on board experience weightlessness and can see the curvature of the Earth.

The booster lands on its own about 4 kilometers from the launch site, and the capsule floats back to the surface thanks to three enormous parachutes that slow it down.

Bezos, who stated earlier this year that he will stand down as Amazon's CEO to focus on other initiatives like as Blue Origin, has indicated that flying into space has been a longstanding ambition of his.