Chris Hemsworth is taking time away from work after receiving a worrying health warning that he called his “biggest fear.”

The 39-year-old Thor star was filming his new docuseries Limitless when he learned that he has two copies of the APOE4 gene – one from each parent – that studies show point toward a predisposition for developing Alzheimer’s disease, per Vanity Fair.

While it’s not a diagnosis, or even a “pre-deterministic gene,” Hemsworth said it does mean he is up to 10 times more likely to develop the progressive dementia-related disease.

It’s also not some abstract concept that he is vaguely aware of. Hemsworth knows too well how Alzheimer’s can affect someone after watching his grandfather, who is currently dealing with the disease.

“I’m not sure he actually remembers much anymore and he slips in and out of Dutch, which is his original language, so he’ll be talking Dutch and English and then a mash-up and then maybe some other new words as well,” he said.

While Limitless explores ways to combat aging and enhance longevity while learning about the body’s limits, Hemsworth was still shocked to received the warning, saying there was an “intensity” to navigating the news.

“Most of us, we like to avoid speaking about death in the hope that we’ll somehow avoid it. We all have this belief that we’ll figure it out. Then to all of a sudden be told some big indicators are actually pointing to this as the route which is going to happen, the reality of it sinks in. Your own mortality.”

The unsettling news shook the Avengers star enough that he plans to take some time away from work and spend quality time with his wife, Elsa Pataky, and their three children: India, Tristan and Sasha.

“It really triggered something in me to want to take some time off. And since we finished the show, I’ve been completing the things I was already contracted to do,” he said, adding, “Now when I finish this tour this week, I’m going home and I’m going to have a good chunk. of time off and just simplify. Be with the kids, be with my wife.”