When Cole Sprouse left Hollywood, he didn’t think he’d ever come back. He was 18, and he’d been acting alongside his identical twin brother since they were in diapers. The choice to work as a kid had not been his own: His single mother wanted to be around for the boys and have a steady career, and putting her twins in the entertainment industry seemed like a “lucrative alternative,” he says now. 

But then Sprouse and his brother, Dylan, landed their own Disney Channel show, “The Suite Life of Zack & Cody.” By 13 they’d signed a licensing agreement with Dualstar Entertainment Group, Mary-Kate and Ashley Olsen’s company, to develop their own quarterly lifestyle magazine, ringtones and cologne. They were full-blown teen heartthrobs.

And yet when it came time to apply for college, the twins decided — unlike fellow Disney stars Miley Cyrus, Selena Gomez or the Jonas Brothers — that they wanted to pursue higher education and enrolled at NYU.

“My brother and I were getting recognized a lot. It became one of those things that we realized we had just sort of taken as gospel since we were little kids, and that there was another path through life,” Sprouse, now 26, recalls. “I was completely content, at the time, to let the Disney shows exist within this little nostalgic bubble and I was ready to move on.”

But somehow here he is now, sitting on the balcony of a ritzy hotel smoking Marlboros, promoting his first leading role in a movie, “Five Feet Apart.” And the film, a romantic drama about two young lovers with cystic fibrosis, is not the only project he’s taken on since graduating with honors from NYU in 2015. For the past two years, he’s starred as Jughead on the CW series “Riverdale,” a teen drama based on the Archie comics.

The program, which has already been renewed for a fourth season, has reignited Sprouse’s popularity. On Instagram, he has nearly 24 million followers, many of whom are obsessed with tracking his real-life relationship with his on-screen love interest, Lili Reinhart.

“Riverdale” also rekindled Sprouse’s love for acting. During college he did none of it, opting to study something completely different: archaeology, geographic information systems and satellite imaging. He became interested in the field because his grandfather was a geologist and “it seemed like an academic discipline that was really competitive and challenging. I fancied testing if I could do something like that.”

He traveled to Germany, France and Bulgaria for excavations, and on one dig, after spending six weeks hunched over a 1-by-1-foot trench of dirt with a toothpick, he pulled a 35,000-year-old Aurignacian stone blade out of the ground. Following graduation, he began working in cultural resource management as an archaeological assistant in a Brooklyn artifact laboratory. He was thinking about going into academia: studying at graduate school, researching a specific time period or peoples and becoming a professor.

But then he heard from his acting manager, who, per Sprouse’s request, had left him alone during his four years at NYU.

“He asked me to come back for a single pilot season. I was on this path, but I said ‘OK, if I don’t book anything, I don’t think I want to do acting anymore,’” he says. He did book something — “Riverdale” — and soon began to realize it wasn’t acting itself he had an issue with.

“From a very young age, the industry had been defined as a business,” he continues, “and it took me going away to school for a while and redefining that to find (performing) as a passion again.”

When it came to tackling his first adult movie part — he and his brother were in Adam Sandler’s “Big Daddy” as boys — Sprouse didn’t want to stray too far outside of his comfort zone. Recognizing the persona he’d established on “Riverdale,” he chose to play a similar archetype in “Five Feet Apart”: Will, a brooding teenager whose rebellious spirit attracts his romantic interest, played by Haley Lu Richardson of “Split” and “Support the Girls.”

“This role was interesting in a larger business sense, because a return to film also meant a question of how much of (the ‘Riverdale’) audience would turn out,” says Sprouse. “I didn’t want it to feel so incredibly distinct.”

The CBS Films production, out Friday, follows two CF patients as they fall in love but are unable to physically touch due to risk of cross infection. Cystic fibrosis is a genetic, progressive disease that affects lung function, making it difficult to breathe; the average life expectancy for the 30,000 afflicted in the U.S. is 37.5 years.

Sprouse showcases some of his work on his Instagram account, which he admits is “very curated.” He’ll often delete old photos of himself, and he’s careful not to post too many photos of his girlfriend, Reinhart.

“I’ve girded my private life very intentionally,” he says. “It’s one of those things that I still sort of grapple with, and Lili and I grapple with.”

Asked if he thought about how much attention dating his costar might garner, he says he had no choice in the matter: “We legitimately could not stay away from one another.”

Beyond Reinhart, he and his cast mates — who film in Vancouver — are exceptionally close, especially of late, as they grapple with the loss of “Riverdale” costar Luke Perry.

“It’s been very, very hard this week,” he acknowledges, referring to juggling his film press responsibilities with his grief. “But the family has asked us all to keep it as private as possible, and I respect them tremendously through this time, so I continue to do so. We go back tomorrow, and it’ll be nice to be together. We all got together and talked it out a couple days ago, and then they gave us a couple of days off of production to acclimate, which was really wonderful.”

As for his future as an actor, Sprouse says he doesn’t expect to leave Hollywood again any time soon.

“It’s easy to forget, because this industry has so many different sides to it, that the act of acting is an incredibly enjoyable thing,” he says. “It’s a really empowering thing to do and it’s all the stuff on the outside of it — the publicity and the celebrity — which I actually had a problem with.”

If you go

FIVE FEET APART

PG-13

Starts Friday at Niantic. Starts tonight at Waterford, Stonington, Westbrook, Lisbon.