Chris Hemsworth is opening up about eye-opening news he learned about while filming his new series, "Limitless."

The "Thor" star, who puts his physical and mental strength to the ultimate test in the National Geographic show airing on Disney+, is sharing that he may have a higher risk of developing Alzheimer's than the general population after undergoing extensive bloodwork.

In a clip from the episode on brain health, Hemsworth takes a genetic test and meets with longevity specialist Dr. Peter Attia who tells the actor that he has two copies of APOE4, or the apolipoprotein E gene, which is the strongest risk factor gene for Alzheimer's disease, according to the National Institute of Aging.

PHOTO: Chris Hemsworth crouches by the edge of a pond on a hike in Episode 5 of "Limitless with Chris Hemsworth".
National Geographic for Disney+
Chris Hemsworth crouches by the edge of a pond on a hike in Episode 5 of "Limitless with Chris Hemsworth".

However, genetic testing for Alzheimer's is in its early days, and not recommended for everyone.

In fact, the National Institute of Aging cautions against genetic testing for most people because a positive test doesn't necessarily mean that you will develop Alzheimer's and can cause undue stress and anxiety. But Dr. Attia points out that for anyone -- no matter their genetics -- making healthy choices can help reduce the risk of Alzheimer's later in life.

What is APOE4?

According to the NIA, certain genes might increase the risk of developing dementia, including Alzheimer's disease. The most significant of these is APOE4.

About 25 percent of people carry one copy of APOE4 and two to three percent carry two copies, according to the NIA, one APOE allele each from their biological parents.

In Hemsworth's case, doctors found two copies of APOE4 in his DNA, saying that he has a set of APOE4 from his mom and a set of the gene from his dad, making his risk for developing Alzheimer's several times higher than most people, according to one study.

While APOE4 increases the risk for Alzheimer's disease and is associated with an earlier age of disease onset, the NIA says that it does not mean a person will definitely develop the disease.

"The idea that I won't be able to remember the life I've experienced, or my wife, my kids, is probably my biggest fear," he says in a clip from the series.

In another clip, Hemsworth reflects on his grandfather's battle with Alzheimer's and talks about how hard it is.

"He is a beautiful man," Hemsworth said. "He either doesn't remember who we are, you know, his grandchildren, but also even his own children he forgets. It's heartbreaking."

Research shows that developing the disease is more likely for those who do have a first-degree relative with Alzheimer's, but having a parent or sibling with Alzheimer's does not always mean that someone will develop it.

PHOTO: In this June 11, 2022, file photo, Chris Hemsworth arrives at an event in Sydney, Australia.
Lisa Maree Williams/Getty Images, FILE
In this June 11, 2022, file photo, Chris Hemsworth arrives at an event in Sydney, Australia.

Path to preserving brain health

While Hemsworth is met with the life-altering news in the show, a doctor in one clip points out that the learned information is a blessing and can help motivate Hemsworth to look after his brain health.

"It's my belief that if we take every step possible, we can reduce your risk to that of anyone else," Attia tells Hemsworth in a clip.

There is currently no cure for Alzheimer's disease, but the Centers for Disease Control and Prevention says there are ways to reducing the risk of Alzheimer's, including regular exercise, managing blood sugar and maintaining a healthy weight. Other ways that the CDC says Alzheimer's can be prevented include quitting smoking, avoiding excessive drinking and getting enough sleep.

"It very quickly just became another wonderful motivation to make some changes and arm myself with all the tools to live a healthier, better life," Hemsworth said while appearing on "Good Morning America."

He continued, "I think any of the motivations for living better can come in many shapes and forms and this was, you know, whatever I'm going to do now to benefit and protect myself from brain health will benefit every aspect of my health and well-being."

"Limitless" is now available to stream on Disney+.

Disney is the parent company of ABC News and "Good Morning America."