When US talk-show host Jimmy Kimmel interviewed the “God of Thunder from Down Under” to talk about his new stuntman-style docuseries Limitless, Chris Hemsworth didn’t hold back.

Filming the whole six-part Disney+ series was “one of the most intense things” he’d ever done, he told the late-night ABC America show on Tuesday.

As new photos reveal how he “digitally aged” 50 years in episode four, the Thor: Love and Thunder superhero star, 39, said the Marvel franchise stopped him working on the show after he was injured during one of the extreme scientific challenges.

Referring to a rope climb where he had to be lean but strong, he recalls to Kimmel: “Great, we’ll do it before I shoot Thor. Anyway, I started training, I blow my ankle out, and Marvel stepped in.”

“[They] said: ‘No. The show that might kill him. You can do that after our film.’”

Hemsworth agreed to be the guinea pig for the Darren Aronofsky-directed series for National Geographic, to go on a rollercoaster personal journey to explore how to combat ageing, and in the process discover the full potential of the human body.

His so-called challenges were confronting and scientifically crafted – he balances on narrow beams outside skyscrapers, dives deep into icy waters off Norway with his brothers Liam and Luke, and dangles off a single rope suspended from a cable car.

If he didn’t succeed in the challenge, he quips, “if I fail this, and don’t commit to this stunt, there’s no episode … or I die, yeah”.

But, it all comes to a head in episode four, called Acceptance, where Hemsworth faces his most extreme and confronting challenge.

He dons a heavy “ageing suit” and spends three days in a retirement village.

The production crew digitally enhance his features (not studio make-up), to see what he’d look like as an older man.

In fact, the most extreme recreation of himself is at 90 years old (Spoiler alert: Swipe through his Instagram images to see him as the old man).

Wincing

In an interview with Vanity Fair, which gained exclusive access to the digital images, he didn’t like what he saw.

“No. I was like, Oh, hmm … yeah,” he says, adding his wife didn’t run for the hills, “which was good”.

His wife Elsa Pataky, who also participated in the episode, went through a physical “ageing-up process” to surprise him for one sequence at a dance.

In the scene, she turns around to reveal how she might look decades from now.

What happens next will be for the series to reveal, but suffice to say he doesn’t “run for the hills” either.

“They posed for a photo together—her in the age make-up, and him looking like he does now—then the producers digitally aged him up as well for a second image,” VF reported.

Hemsworth said scrolling through the shots, he looks at the one “depicting him at his thinnest and most weathered”: “That one…” he says, wincing.

“Took my hair away.”

Vanity Fair got an advanced look at the ageing Hemsworth couple. Photo: Vanity Fair/By National Geographic for Disney+

Why?

According to the official Disney+ synopsis, “he’s testing the theory that the best way to combat ageing and fear of mortality might not be to fight it but accept it”.

“He takes up a gauntlet of physical and mental feats designed by world-class experts, scientists and doctors to unlock different aspects of the ageing process.”

The other five episodes – years in the making – are titled Shock, Fasting, Strength, Memory and Stress-proof.

“Each meticulously crafted challenge is rooted in game-changing science, drawing on new research and long-held traditions.”

Tweet from @liamhemsnewss

Hemsworth’s mission, which he accepted, was to “understand the limits of the human body better and discover ways we can all extend health and happiness into old age”, Disney says.

They bring in a bunch of experts to talk him through what lies ahead for each episode.

To help him combat his mind’s ageing process? Introducing Dr Sharon Sha, a doctor and clinical associate professor and associate vice-chair of clinical research neurology and neurological sciences for Stanford Center for Memory Disorders.

What about guiding him on old age and mortality? Let’s go to president and counsellor at Mettle Health, Dr B J Miller.

And the big one … talking about his death? None other than Alua Arthur, a death doula and founder of Going with Grace.

Why he wanted to go on the show in the first place is a no-brainer.

Hemsworth tells Kimmel his family, especially his father, Craig, asked him that very question.

“To live longer,” he said.

All six episodes of Limitless on Disney+ on November 16