Ashton Kutcher has revealed that he had vasculitis, a rare autoimmune disease that affected his ability to see, hear and walk.

In a preview clip of an upcoming episode of the National Geographic’s Running Wild with Bear Grylls: The Challenge, the Two And A Half Men star said he was “lucky to be alive” following his battle with the condition.

“Like two years ago, I had this weird, super rare form of vasculitis, that like knocked out my vision, it knocked out my hearing, it knocked out like all my equilibrium,” he told Grylls. “It took me 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,’” he said.

The actor went on to say that he saw the health scare as “thing that [was] made for” him, which helped to give him a new perspective on life.

Kutcher first rose to fame on the comedy series That ’70s show, in which his wife and fellow actor Mila Kunis also starred.

In May this year, it was announced that the couple the will be reprising their roles as Michael Kelso and Jackie Burkhart for the upcoming sequel series, That ’90s Show.

They’ll guesting in the new series alongside previously announced stars Kurtwood Smith and Debra Jo Rupp, who will reprise their roles of Red and Kitty Forman, respectively.

That ’90s Show will also see guest appearances from Topher Grace, Laura Prepon and Wilmer Valderrama who all starred in the original sitcom which ran from 1998 to 2006.

The upcoming sequel series will be set in 1995 and, according to Netflix, will see Leia Forman (Callie Haverda), daughter of Eric (Grace) and Donna (Prepon) visit her grandparents for the summer, where she bonds with a new generation of Point Place kids under the watchful eye of Kitty (Rupp) and the stern glare of Red (Smith).

“Sex, drugs and rock ’n roll never dies, it just changes clothes,” said the announcement.