What’s a teenager to do after wowing four celebrity judges and 12.7 million television viewers and 2.5 million YouTube watchers — on “America’s Got Talent?”

Take the English Regents of course.

First, congratulations were in order for Christian Guardino at Patchogue-Medford High School on Wednesday, just hours after the outgoing junior’s sensational singing performance on national television.

“Everybody was so happy for me and complimenting me,” Christian, 17, told GreaterPatchogue. “The security guards, when they were checking cell phones, would say, ‘We saw you on ‘America’s Got Talent!’”

Then Christian sat for two hours and took a state exam.

“I feel like I did pretty well,” he said.

But when he put his pencil down, no golden confetti fell from the rafters.

That’s what happened when he finished belting out “Who’s Lovin You,” and Howie Mandel slapped the golden buzzer Tuesday night on TV, meaning Christian won’t have to audition anymore in the competition.

His next step will be to perform on the live shows that start Aug. 15.

ALWAYS SINGING

It was clear early on that Christian had a gift — way early on.

His mom, Elizabeth, recalls him successfully humming “Twinkle Twinkly Little Star” in his bounce seat when he was just a few months old.

“And whenever I would give him a bath as a baby, I would sing scales and he would copy me; he would echo me,” Guardino recalls, still amazed.

Then there were the family parties, when the uncles would bust out their guitars.

Christian, just 1, would start singing.

“He wasn’t making sense, obviously. But he would follow the chord changes,” his mother said. “He would be making up his own words but he would sing bluesy. It was crazy.”

Years later, he would stun a crowd while singing Karaoke at Patchogue’s St. Liberata Festival.

“The people just crowded around him,” Elizabeth said. “It was intense.”

FROM THE DARK

Christian was born into a musically inclined family, but his parents attribute some of his keen awareness to sound and melody to a rare retinal disease called Leber congenital amaurosis, which limited his ability to see.

He was afflicted with the degenerative condition since birth, and at 12 it was worsening. He was told he would go permanently blind. He was fortunate enough to be eligible for groundbreaking surgery through University of Pennsylvania’s Scheie Eye Institute at the Children’s Hospital of Pennsylvania.

He was still just 12 years old. The hope was to prevent his eyes from getting worse. They actually got better.

“Prior to the procedure, he was night blind. There always had to be lights on inside or he would bump into things,” Elizabeth said. “Or at a restaurant he would need a cane or a guide. “

If it wasn’t for the surgery, his mother said, Christian would have had to be led onto the middle of the stage for his “America’s Got Talent” audition, which was taped on March 13, a day before his 17th birthday.

“So to see him walk out onto that stage himself and say, “Here I am!” his mother said, ” … it’s still really amazing.”

THE BIG SHOW

Christian’s first major award came from a performance of the same song, “Who’s Lovin You” by the Jackson 5 at the Apollo Theater in 2014, when he won the contest for his age group.

He last sang at the Apollo in December, when he got another standing ovation.

But he had much work to do before the “America’s Got Talent” tryout in March. This winter he worked on the song with piano prodigy and fellow teenager Matthew Whitaker of New Jersey. 

Whitaker, now a family friend, recently appeared on “The Ellen DeGeneres Show.” The two had met at the Apollo.

“He helped us make the track and the music for ‘Who’s Lovin You,’” Christian said.

The work paid off mightily, because the second Christian jumped into the song, judge Simon Cowell’s eyes went wide and his head snapped to the rest of the judges.

From there, it was on. 

“I was petrified,” Christian admitted Wednesday. “But as soon as I came out with that first note and the judges reacted and everybody started going crazy, I got comfortable.”

Before he knew it, the confetti was falling. So were the tears, from Christian, from mom, and in the audience.

Three months later, the rest of the country got to experience what happened that night in Los Angeles. Especially at PeraBell Food Bar in Patchogue, which is co-owned by Christian’s uncle, David Chiarella.

PeraBell hosted a viewing party packed with family and friends. There many moist eyes there, too.

“Including mine,” Christian laughed.

THE AFTERGLOW

At first he and his mom tried to respond to the trickle of kind words and well-wishes being left by strangers Tuesday night on the Christian Guardino Facebook fan page.

And then, the avalanche.

“Then we said, we couldn’t possibly respond to everyone,” Elizabeth said.

Christian’s Facebook fans tripled in a matter of minutes, then overnight jumped from around 500 to 16,000.

The amount of national news stories being written about him amounts to the hundreds.

The headlines include:

Watch This Unassuming Teen Blow Away the America’s Got Talent Judges (TIME)

Try not to cry watching Christian Guardino’s ‘America’s Got Talent’ audition (USA Today)

‘Sweet 16-Year-Old Singer Absolutely Slays His Way to Golden Buzzer (TheWrap)

“As a parent you’re going to believe in your child,” Elizabeth said. “And I’ve been around music long enough to know he was truly talented, but to have that affirmation come from people who are complete strangers, and in those numbers …

“I’ll be honest, I’m having a hard time wrapping my head around it.”

Christian called the whole thing “really insane.”

“People are complimenting me, videos are getting millions of views,” he said. “It’s overwhelming, but in a positive way.”

They both appreciate the support they’re getting from the community and beyond.

“His story in itself was something we always felt needed to be shared, and to see the reception like this,” Elizabeth said, “it’s confirmation that this is what he was meant to be.”

Next, he’ll be practicing for the August performances, and more national attention.

After the Regents.

Top Photo: Christian Guardino at “America’s Got Talent.” in L.A. (Facebook)