Meet Mariah Yeater — the baby mama who rocked Justin Bieber’s world with bombshell claims that he got her pregnant during 30 seconds of backstage passion after confessing he was a virgin.

Yeater — who’s demanding a DNA test from the teen heartthrob — claims they had a super quickie on a “shelf’’ in a bathroom of an LA arena, where she said he talked dirty before having sex for the “first time.’’

The unemployed, 20-year-old Yeater — who was excoriated by boatloads of “Beliebers’’ on Twitter yesterday — stated in a San Diego court filing on Halloween, “I had unprotected sex with Justin Bieber following a concert that I attended at the Staples Center in Los Angeles, CA on Oct. 25, 2010. On July 6, 2011, I gave birth to a baby boy.

“I believe that Justin Bieber is the father of my baby.”

PHOTOS: JUSTIN BIEBER

Yeater estimates she’ll need $12,000 per month in child support from the singing sensation. Bieber has been ordered to appear in court Dec. 15 to respond to the allegation.

Bieber posted a Twitter response yesterday: “So Im going to ignore the rumors . . . and focus on what is real. an opportunity to help by doing what i love. Judge me on the music! Love yall.”

Reps for the star — who is dating Disney singer-actress Selena Gomez — called Yeater’s claims “malicious, defamatory and demonstrably false.’’

His fanatical follower, meanwhile, used much more colorful language on Twitter.

“Mariah Yeater, you messed with the wrong person & fanbase!” tweeted iJBDSupport. “BELIEBERS BELIEVE IN JUSTIN and we’ll always believe in him so go away . . . famewhore.”

Another ticked-off tweeter, @CantBeliebIt, wrote, “Mariah Yeater sounds like a disease.”

@SessyKidrahl got even nastier: “Dear Mariah Yeater, Roses are Red, Violets are Blue Stay away from Bieber or the Beliebers will KILL YOU.”

Pointing out that Bieber, 17, makes $4.5 million a month, Yeater stated in court papers that she gets food stamps and welfare totaling about $500 per month and has just $400 in the bank. She owes the hospital where she gave birth $25,000.

Yeater gives a salacious blow-by-blow in court filings of how her son, Tristyn Anthony Markhouse Yeater, was conceived during a half-minute wham-bam-thank-you-ma’am encounter with Bieber after the concer.

As it turns out, because Bieber was — and remains — younger than California’s age of consent, Yeater’s claim of having sex with him when he was just 16 and she was 19 leaves her open to prosecution for statutory rape.

She writes in the court papers, obtained by Star magazine, that “after the concert I was approached by a security guard who asked if I wanted to meet Justin Bieber backstage. I accepted and followed him backstage.”

Yeater said she waited with several “other young women” before “Justin Bieber appeared and engaged me in conversation.”

“Immediately, it became obvious that we were mutually attracted to one another and began to kiss,” Yeater claimed. “Shortly thereafter, Justin Bieber suggested that I go with him to a private place where we could be alone.

“I agreed to go with him and on the walk to a private area . . . he told me he wanted to make love to me and that this was going to be his first time.

“He also said he would give me his phone number after we had sex and told me he wanted me to be at his future concerts and he would give me backstage passes.”

In the bathroom, Bieber allegedly began “touching” her and repeatedly made vulgar remarks about what he wanted to do to her, Yeater wrote.

“I asked him to put on a condom for protection, but he insisted that he did not want to. In his own words, he said that because it was his first time he wanted to feel everything.’’

The “Baby’’ singer “then quickly took off my clothes and we had sex . . . At the time I was on top of some sort of shelf,” Yeater said. “The sexual intercourse was brief, lasting only approximately 30 seconds . . . He was clearly embarrassed about how the sex did not last very long.”

Yeater wrote that she tried to contact him after she got pregnant, but his representatives never called her back.

Additional reporting by David Ogul in San Diego