It’s been about 37 hours since Harlem’s Just Sam was crowned the new American Idol, and the 21-year-old former subway busker is still getting used to her new title.

“This is definitely unexpected,” Just Sam tells The Post from the West Hollywood apartment where she’s been on lockdown. “It’s only been one day, so . . . it’s been wild.”

The first LGBTQ “Idol” champ, whose real name is Samantha Diaz, was raised by her grandmother in Manhattan’s Frederick Douglass Houses, where residents held a viewing party for the show’s finale.

But because of coronavirus concerns, Just Sam was unable to fly back to be with her grandmother after her victory.

“I plan on flying back out there and quarantining for 14 days,” she says. “And then I’ll go check in with Grandma. And I might be staying for a couple weeks — just because she told me that she misses me.”

Just Sam was adopted — along with her older half-sister Anabelle — by her father’s mother, Elizabeth, at age 6 because her parents were not able to take care of her. But the musical spirit kept her going from a young age.

“When I was younger, and my grandmother had first adopted me and my sister, we used to put on little shows for her in the house,” she says.

When she got to middle school — at Global Scholars Academy — a teacher noticed she had something special when she sang Alicia Keys’ “Un-thinkable (I’m Ready)” for an audition. “My teacher in sixth grade told me that my voice gave him chills when I was auditioning for a talent show,” she says. “And I had never heard that before that day . . . So from that moment on, I’m like, ‘Wow, I guess I really can sing!’ ”

It was around that time that Just Sam found her own stage on the subway. “I started with my sister Anabelle and my friend Tiffany,” she says. “We would meet up after school . . . We made, like, $100 one day, and we were like, ‘What?!’ ”

It didn’t take long, though, before Just Sam wanted to break out and go solo.

“I started to sing by myself a couple months in, ’cause for me it became about not wanting to ask my grandmother for money,” she says. “The 1 train was one of my go-to’s. But then there’s the C, the B. Honestly, you could catch me — or, you could have — on any line except for the 4, 5 and 6. And that’s just because there was really no money there. Going on the train, it was, like, either too crowded or the people were too angry coming from work.”

Growing up in Harlem, Sam would hear songs such as Marcia Griffiths’ “Electric Boogie,” but, she says, “We didn’t really get to enjoy the neighborhood parties until we got old enough to stay out after the street lights went on.”

Instead, she and her sister would take long walks out of Harlem with their grandmother. “We would go down to 42nd Street and 34th Street,” she says. “We would literally walk from uptown all the way down to Burlington Coat Factory downtown [at West 23rd Street] sometimes . . . We would go window-shopping, you know, ’cause we couldn’t really afford anything.”

Not having her parents in her life wasn’t easy. “We had no mother, we had no father,” she says. “So we were, like, teased for that. My mother, we would visit her [in prison] growing up. After she got out of prison, we did try to have a relationship, but that didn’t work out.”

Even throughout her “American Idol” journey, Just Sam has not had contact with either of her parents. “So I’m just waiting on Dr. Phil to help,” she says.

But grit, determination and a love of music — “Listen” by Beyoncé, ”Rolling in the Deep” by Adele and “Fading” by Rihanna were favorites — kept her performing on the trains and would eventually take her to preliminary auditions for “American Idol” at the Brooklyn Expo Center in July 2019.

“I’ve auditioned for ‘The Voice’ before and ‘America’s Got Talent’ in hopes to make it on those shows, and that didn’t happen,” she says. “You know, God’s plan. It was all in his timing.”

Now, she reigns as the the first LGBTQ champion of “American Idol.” “I am a child of God, so that’s always gonna be first. That’s actually the only label that I ever want to have,” she says. “But I like what I like, and that’s just that, you know? And it’s not men. Like, at all.”