Last-minute decisions are not uncommon in TV and film, and Justin Cornwell is living proof. The aspiring actor got the call — congratulations, you’re starring in a new television series — four days before they started shooting the pilot.

That series, “Training Day,” premieres Feb. 2 on CBS. Based on the gritty 2001 film that starred Denzel Washington and Ethan Hawke, this rapid-fire TV version pairs Bill Paxton as Frank Rourke, a grizzled, plays-by-no-one’s-rules-but-his-own maverick cop, with Cornwell as Kyle Craig, his young new partner, who, yeah, may be a bit naive about the choices one must make working the streets of Los Angeles, but — as Rourke soon discovers — is no pushover.

Cornwell, 28, a native of Louisville, Kentucky, studied theater at the University of Louisville and began acting at the Chicago Shakespeare Theater. He’s appeared on “Empire” and “Chicago PD.”

So let’s get something random out of the way first. You’re . . . tall.

You know something . . . [He laughs.] I appreciate you saying that. You’re the first person who ever mentioned it in an interview.

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You’re 6-foot-5, is that right?

Yeah.

So many guys in film or TV are surprisingly short, so it’s kind of refreshing to see someone who’s actually tall.

Well, I fight some guys on this show who are humongous — 7-foot. Ridiculous.

Who was the first person you called when you found out you got cast in your first network series?

My mom. I’m like, “Mom, I can pay you back.” She was like, “Finally!” [He laughs.] No, she was happy for me. They didn’t have the person they wanted, so they hired me four days out. I tend to adapt pretty quickly. But I remember, three days into shooting, thinking, “Wait — I’m a star of a TV show with Bill Paxton.” I almost didn’t have time to get excited about it before the pilot was in the can.

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Have you trained with real police officers?

I was able to hit up LAPD with Bill and we went out in a new division in South Central.

South Central . . . inner-city Los Angeles, for real.

We rode around with cops for an entire shift. They took us to some rough areas. We chased down crackheads, rode up on some gangs.

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Did it give you a new take on law enforcement?

I met . . . a young African-American guy, couldn’t have been more than a couple years older than me, but he looked younger. He’s a police officer. I thought, “This is my character.” He just wants the streets to be better. He told me the only way he could get out — to not be in a gang — was to play sports or be a cop. Those were the only options. I guess . . . they’re not seeing college as an option. Or a vanity career like being an actor.

A major issue for your character, Kyle, is that his father died when he was young. Your own stepfather died a few years ago — do you draw on that for the role?

Absolutely. I was 21, 22 when he died. So I know what Kyle felt — that sense of having your father around . . . then suddenly not around. And I draw on the relationship with my real father — I didn’t meet him till I was 23.

What was that like?

Hard. It wasn’t a bad meeting. It was kind of healing for both of us. I didn’t need much more. It was just nice to have some closure.

OK — new topic — you’ve auditioned for “American Idol”?

Twice.

What did you sing?

My mom drove me to Chicago. We slept in the car. It was snowy, horrible. I sang . . . the song I always sung at that time . . . I was about 16.

Yeah, yeah, I won’t judge.

I sang “You Should Let Me Love You,” by Mario. I didn’t get through the first verse and they said, “Next!”

Nooo . . .

They let the guy with the zebra bodysuit through. I said, “I’ll never audition for ‘Idol’ again — ever.” A few years later they came to Louisville, my town, and I said, “Well . . . they’re here.” [He chuckles.] Sang the same song — all the way through. They said, “Hey, sing another.” Sang three songs, did an interview and I made it to the next round.

And then?

Got cut. Dang it!

Well, I guess things worked out.

Y’know, I love art. Writing, singing, drawing animation. I’ve written some movie scripts. I just want to tell stories. There’s so much you can learn from stories. It would be a dream for any of those things to work out. But . . . I’m living one of my biggest dreams right now. Star of a TV show. I get to have fun.

Not bad.

I got lucky.