Cameron Douglas was born into movie royalty — but his life hasn’t all been glamorous.

The son of movie star Michael Douglas, 75, and grandson of screen legend, Kirk Douglas, 102, Cameron says the pressure could be debilitating at times.

“It’s strange growing up seeing your father and grandfather as giants projected on screens and billboards . . . It’s diminishing to be perceived mainly as someone else’s son . . . How do you compete with Kirk Douglas? How do you live in Michael Douglas’ shadow?” the 40-year-old writes in his new memoir, “Long Way Home” (Knopf), out Tuesday.

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He followed in his father’s footsteps, at least when it came to drugs, only he took a rougher path.

For years, Cameron was a coke and heroin addict, dealing crystal meth and living a life of destruction which led to nearly eight years in prison.

In the book, he recalls a series of stick-ups for which he was never arrested. Once, at a Hollywood motel, he pulled an air gun on the petrified old lady manning the front desk, and demanded she open the cash register. It had a single $20 bill in it.

The Hollywood scion grabbed it.

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“I’m doing it less for the money than for the adrenaline . . . and the bragging rights,” Cameron writes. “I like confusing people, making them puzzle over how someone who came from so much privilege can do such crazy s—t.”

He was arrested in New York City in 1999 for cocaine possession and again in 2005 when Los Angeles cops found heroin and crack in his car. Two years later, he was charged with felony possession of a controlled substance after police pulled him over in Santa Barbara, Calif. and discovered a syringe of liquid cocaine.

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In 2009, Cameron was dealt his biggest blow when he was arrested during a sting at the Gansevoort hotel in Manhattan. He pleaded guilty to heroin possession and conspiracy to distribute drugs and was sentenced to five years — only to be slapped, in 2011, with four and a half more years for possessing items that tested positive for cocaine and heroin, which he scored from fellow inmates.

Cameron had been exposed to the party scene most of his life.

He writes about the bevy of stars who would live it up at the family home: Jack Nicholson, Pat Riley, Oliver Stone, Danny DeVito.

“Even as a really young kid, I remember running joints back and forth,” he says in the book. “Dad would say, ‘Hey, bring this over to your uncle,’ and I would, not realizing until years later what it had been. As I got older, I would creep from house to house on the compound, climbing balconies and seeing more than I was supposed to: beautiful grown-ups doing the things that beautiful grown-ups living lives of excess do.”

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Once Michael’s famous friends had left their rooms, Cameron and his own pal would rifle through the stars’ bags looking for whatever substances were responsible for the wild night before.

Cameron recalls how, after nights like those, his dad would take him for early morning breakfasts at a Sunset Boulevard hotel; it was only as an adult, he writes, that he realized those father-son moments were actually when Michael was coming down after a long night of partying.

The movie star’s wild life was long a point of contention between Michael and Cameron’s mother, Diandra.

“When I was seven and we were in Aspen, [my mother] held up a little plastic bag with what looked like the dried flowers she used to make the bathroom smell nice . . . ‘Do you know what this is, Cameron?’ This is a drug. Your father is using drugs,’ ” he writes.

Michael and Diandra’s marriage was tumultuous from the get-go.

For her 21st birthday, in 1979, Michael threw her a raging bash at their home in Beverly Hills — despite the fact that she had tonsillitis.

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“Dad didn’t cancel the party, and while she lay ill in bed upstairs, he partied downstairs with [the band] Foreigner and other guests, nearly all of them his friends. Finally, at 5 a.m., Mom kicked every one out,” Cameron writes. “Afterward, she decided she didn’t like show business or the people in it. This would be a problem, since that was Dad’s life.”

Their father-son bond was also often strained, due in part to Michael’s career.

“Our relationship was a series of jump cuts, vivid bursts when we were together punctuating longer stretches when we were apart,” Cameron writes.

One summer, Michael decided that Cameron needed a “more constant male influence.”

During a lunch with Diandra, at the Ivy in Beverly Hills, Michael pointed to a busboy.

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“Dad said, ‘What about this guy? He seems very capable. He could be a houseman or something like that.’ Mom spoke to him in Spanish . . . he was from El Salvador,” Cameron writes. “Soon [he] was living with us. He took care of me from the moment I woke up to the moment I went to sleep.”

Cameron, age 10, was heartbroken when the former busboy told him he was leaving.

“I’d later learn that Mom had found vodka bottles under [his] bed and asked him to stop drinking,” he writes.

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Cameron had just started at boarding school when he heard that his father had checked into rehab for “sex addiction.”

“As far as I could tell, he was there mainly for his drinking and to placate Mom. She had caught him in bed with another woman, given him an ultimatum that he had to deal with his drug and alcohol intake, and two weeks later he checked into Sierra Tuscon, a clinic in Arizona,” he writes.

Michael continued to stray and, in the summer of 1995, Diandra reached her breaking point after a private investigator caught the star at the Beverly Wilshire hotel with yet another woman.

“It’s sad to think back on, but when they told me they were getting divorced, it didn’t knock my socks off. Actually, I welcomed it,” Cameron says in his book.

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At one point, before Cameron’s prison sentence, Michael told his son that it was impossible to nurture a relationship with him.

“I think you’re going to overdose, or someone’s going to kill you, or you’re going to kill someone. I’m trying to prepare myself emotionally,” Michael said, according to the book.

Despite the familial ups and downs, Cameron was elated when Michael and Kirk, whom Cameron calls “Pappy,” visited him at the Metropolitan Correction Center in Manhattan while he awaited sentencing in 2009.

“I’m so impressed by Pappy, and touched. He’s ninety-three, and he’s come all the way from California to see me,” Cameron recalls in the book.

Kirk asked him: “You’ve been getting in any fights?”

Cameron told him yes.

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“Have you been winning or losing?” Kirk asked.

“Winning,” Cameron responded.

“That’s my boy.”

While in prison, Cameron commissioned a huge tattoo on his torso of his grandfather and father.

“I’ve never been able to overcome my conflicting feelings about my last name, my pride in it and at the same time, my discomfort with having it define how other people see me,” he writes.

“When I get their faces tattooed on my body, I feel ready, finally, to show an uncomplicated pride in them. When I show the tattoo to Dad, he seems embarrassed.”

After being released from prison in 2016, Cameron moved into a Bronx halfway house and, later, into a Tribeca apartment with his girlfriend, Viviane Thibes, a yoga instructor.

He writes about traveling to California to visit Kirk, who, at 100, is taken with his grandson’s tattoo and grills him about life in prison.

“Every time a guest comes over, Pappy calls me over and has me show off my abs,” Cameron writes of the “Spartacus” star.

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“He has so much curiosity, asking endless questions about prison life. ‘Were you in a gang? Did you fight a lot? Did you kill anyone?’ ”

Cameron credits his dad’s second wife, actress Catherine Zeta-Jones, with “pushing [Michael] to extend his paternal love to me.

“One day, we’re hanging out and [my dad] says, ‘I don’t know how you did it. How you went through the things you did.’ It’s the first time he’s ever acknowledged it quite like that,” Cameron writes.

Now, he’s a father himself. In December 2017, Viviane gave birth to their daughter, Lua Izzy Douglas. They live in the Hollywood Hills and Cameron is pursuing a career in acting — and rebuilding a relationship with his family.

“[My father and I] never really became friends, as many father and sons do at a certain point, but now we’re starting to do that,” Cameron writes.

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“We’re forming the relationship I’ve always wanted.”

This article originally appeared in Page Six.