Spanish endurance athlete Kilian Jornet is famous for a lot of things: winning the hardest trail and ski-mountaineering races in the world, making daring (and speedy) alpine ascents, and holding the fastest known time on mountains across the globe.

But possibly Jornet’s biggest—and most fiercely disputed—accomplishment is his back-to-back summit of Everest in 2017. That May, he went to the top of the world’s highest mountain twice—without supplemental oxygen or fixed ropes, and within a single week. At first, his team claimed Jornet had set a new fastest known time on the mountain. That turned out to not be true—Jornet later said he never claimed a fastest known time , and that his media team had made the error when they rushed out a press release. But even without breaking the record, Jornet’s accomplishment of summiting Everest back-to-back—despite getting lost on the mountain’s north face on the way down from his second summit—and then winning several ultra-running competitions that summer, stunned fans worldwide.

The plot thickened when a climber in Oregon circulated a 19-page document that questioned whether Jornet actually summited Everest either time that May. The climber zeroed in on the uncertainty surrounding Jornet’s documentation, specifically the GPS data and images of the summit. Jornet responded to the allegations thoroughly in an interview with Outside—the GPS data is complicated, but explicable, he said. As for the inconclusive photos, “It was hard to film,” Jornet said. “It’s the last thing I was thinking about.”

This fall, Jornet is going back to Everest, though this time, he’s keeping his plans close to his chest. When reached for comment, his spokesperson said that, “Unfortunately, Kilian hasn’t planned to talk to the press at this moment. If he completes any relevant activity, he will communicate about it once he’s finished.”

What we do know is that before attempting Everest, Jornet intends to lead a three-member team to the top of Lhotse, Everest’s neighboring peak and the fourth highest mountain in the world. Jornet’s permit to summit Everest is one of two permits granted for the autumn season, as was first reported by The Himalayan Times.

If Jornet does set a record, there’ll hopefully be better proof this time.