Action hero Arnold Schwarzenegger does not do self-doubt.

It is 35 years since he swaggered, naked as the day he was born, into movie history as The Terminator.

Now 72 and just a year on from a life-saving heart op, the star reckons he is buff enough to reveal all again.

Grinning tightly, he insists: “I can still do that. I can still arrive naked.” You won’t hear Schwarzenegger confessing to anxiety or inner demons.

Though he nearly died on the operating table when a routine procedure went awry, his only worry was that it might mess up his filming schedule.

And the former bodybuilding champ was back in the gym within a week of returning home from the hospital.

Now Schwarzenegger has reunited onscreen with actress Linda Hamilton for the first time since 1991’s Terminator 2: Judgment Day.

"Terminator: Dark Fate" hits cinemas tomorrow — the sixth installment of the hit science-fiction franchise. Arnie’s return to the role of a deadly cyborg required as much stuntwork as ever.

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“It’s no problem,” he insists in our exclusive interview. “It gets a little bit harder the older you get. The body is not as forgiving as it used to be.

Actor Arnold Schwarzenegger speaks during Paramount Pictures exclusive presentation during CinemaCon at The Colosseum at Caesars Palace on April 04, 2019 in Las Vegas, Nevada. CinemaCon is the official convention of the National Association of Theatre Owners.

Actor Arnold Schwarzenegger speaks during Paramount Pictures exclusive presentation during CinemaCon at The Colosseum at Caesars Palace on April 04, 2019 in Las Vegas, Nevada. CinemaCon is the official convention of the National Association of Theatre Owners. (Photo by Gabe Ginsberg/WireImage)

“But you just have to train more, you have to do more reps. That’s what it’s all about.”

Fans are lucky he is back at all. In March 2018, an op to replace a faulty pulmonary valve in his heart left Arnie needing emergency surgery.

“It was kind of a surprise,” he says with typical understatement. “I never get scared about these things.

“For a minute I was worried it was too close to doing 'Terminator 6' ('Dark Fate') but I realized right away the movie is a good means to get back into shape again.

“I was home in no time and was back to the gym in no time. Most people baby themselves too much after surgery.”

Arnie had to give the bench presses a miss, as his rib cage was being held together with wire. But within four months of the op, he was on set.

Schwarzenegger had another reason to be fit and well: The marriage of his eldest daughter Katherine, 29, to "Guardians Of The Galaxy" star Chris Pratt.

Schwarzenegger says of the June ceremony in LA: “It was a beautiful wedding. We couldn’t have picked a better guy. Chris is fantastic.

“He’s a jewel — a gentleman and a hard-working guy. He’s talented. He’s a sweetheart. They fit well together.” The actor was joined at the ceremony by Maria Shriver, who Arnie wed in 1986.

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They split in 2011 after he admitted fathering a son, Joseph, with their housemaid. The divorce has still to be legally finalized.

Today the movie icon posts online about his love for Joseph, 22, as he does for his other four children. He says: “Children are precious.

“It’s wonderful to watch them grow up, wonderful to watch them be successful, to reflect on the early days when you were teaching them things, discipline or sports or things like that. We all have a really great relationship.”

He and Pratt, 40, bonded by pumping iron together. His son-in-law had to ditch the love handles to play comic-book hero Star-Lord in Marvel’s "Guardians Of The Galaxy" movies.

And Schwarzenegger says: “The audience — the fans — want an action hero who looks like one.

Circa 1967: Studio portrait of Austrian-born bodybuilder Arnold Schwarzenegger flexing his torso in an advertisement for a German protein product.

Circa 1967: Studio portrait of Austrian-born bodybuilder Arnold Schwarzenegger flexing his torso in an advertisement for a German protein product. (Getty)

“Everyone has to have ­muscles. Everyone has to have deltoids and abs and a six-pack and move in a certain way and be believable.

“The days of the 1950s, when guys were skinny and played the action hero, are over. What we created in the Eighties with muscles is now required.”

The Austrian-born superstar was 14 when he decided to become a bodybuilder.

At 19, he flew to England to train for the Mr. Universe competition in London — a contest he won three years in a row from 1968 to 1970.

Unable to speak the language, Arnie arrived having memorized a single unlikely phrase.

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He says: “This was where I learned my first words in English, ‘335 Romford Road.’ That’s where I stayed with a family.”

He moved to the US and would claim the prized Mr. Olympia title seven times, including six wins in a row.

Arnie says: “As an immigrant, it was all about ­becoming rich and famous.”

The movie "Pumping Iron" went behind the scenes of the 1975 contest — and showed Arnie’s ability to wage psychological warfare against his rivals.

He found real fame with 1982’s "Conan The Barbarian" and became a movie icon in "The Terminator" two years later.

He racked up a string of box- office hits including "Commando," "Predator" and "Total Recall."\

Arnie candidly admits his main ambition in Hollywood was to bank millions rather than win acting awards.

He says: “'Terminator' became one of Time magazine’s top ten movies of the year. It was amazing, especially for what they felt was a cheap B-movie.

Cast member Arnold Schwarzenegger poses by a Terminator replica at the premiere of

Cast member Arnold Schwarzenegger poses by a Terminator replica at the premiere of 'Terminator Genisys' in Hollywood, California June 28, 2015.  (REUTERS/Mario Anzuoni)

“So I really could chase my goal of being the highest-paid ­entertainer in the world.”

After scaling that particular peak, Arnie switched his sights to the political arena. In 2003, he ran as a Republican to become Governor of California.

Yet again, he won — and served the maximum two four-year terms. Having already amassed millions, he turned down the post’s more than $172,500 annual salary.

Arnie says: “When I became governor, I sacrificed ­having any income because I didn’t do any movies for seven years.

“I had made $20 million a movie and made two movies a year. But I didn’t mind that. It was more important to be governor.”

There have been setbacks along the way, including the very public break-up of his marriage and some bruising movie flops.

Those include the notorious 1997 turkey "Batman And Robin," in which Arnie played Mr. Freeze opposite George Clooney’s Caped Crusader.

But Arnie doesn’t do self-pity any more than he does self-doubt. He says: “I have never had any dark moments.

“I am very lucky that I had a very clear vision about what I wanted to achieve and accomplish. Most people don’t have that.

“That’s why most people are searching for some answers, for some truth. They read self-help books on how to be happy. I don’t have that.”

The star became a US ­citizen in 1983 but cannot run for President because he was not born in America. Then again, Arnie is busy enough as it is.

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He reels off a dizzying list of activities, including organizing the Arnold Classic bodybuilding events across six continents, funding the Schwarzenegger Institute at the University of Southern California — which promotes non-partisan co-operation on major issues — and backing environmental issues.

Arnie says these days he has switched to a mostly vegan diet while his transport of choice is a bicycle or an all-electric Hummer.

He says: “I am on a crusade worldwide to reduce greenhouse gases and not have seven million people die a year from pollution.”

But he is not ready to retire from the big screen yet. In a reversal of his most famous line from the Terminator movies, Arnie says in "Dark Fate:" “I WON’T be back.”

This article originally appeared in The Sun.