Ashton Kutcher said he’s “lucky to be alive” after a private battle with a rare autoimmune disorder took away his sight, hearing, and some of his motor control two years ago. The 44-year-old actor revealed his diagnosis in a forthcoming episode of Running Wild with Bear Grylls: The Challenge, a portion of which was broadcast by Access Hollywood on Monday. “I had this weird, super rare form of vasculitis that knocked out my vision, it knocked out my hearing, it knocked out like all my equilibrium,” Kutcher told Grylls. “It took me about a year to build it all back up.” He added: “You don’t really appreciate it until it’s gone. Until you go, ‘I don’t know if I’m ever going to be able to see again, I don’t know if I’m ever going to be able to hear again, I don’t know if I’m ever going to be able to walk again.’” Of his guest, Grylls reflected, “What do they say in survival? ‘Storms make you stronger.’ And I think he’s living proof of that.” The episode of Running Wild is set to air next Monday on National Geographic.