Nostalgia just slammed into Vegas ... 'cause when New Kids On The Block kicked off their Right Stuff residency, members of a rival boyband crashed the stage -- and the crowd lost it!

Catch the clip -- NKOTB were hyping up the crowd last weekend at the Park MGM, asking who wanted to marry them back in the '90s … and while fans screamed, Backstreet Boys’ Howie Dorough popped up with a cheeky banner that read, "I Do."

Howie later pulled up with AJ to crash the stage ... and it was nothing but boy band bromance -- hugs, laughs, and major 1990s nostalgia as they embraced NKOTB like long-lost brothers.

If you were expecting a boy band showdown -- think again. Even with BBs launching their Millennium Sphere residency later this month, both groups proved there’s more than enough room (and love) to go around on the Vegas Strip.

But with NKOTB already kicking things off with a bang, you can bet it’s lit a fire under the Backstreet Boys -- and sources tell us they’re grinding hard, rehearsing 12 hours a day, 5 to 6 days a week, to gear up for their massively anticipated Sphere takeover.

There's a new K-pop boy band on the block ... and AHOF tells TMZ they dream of starring on one of the biggest stages in America -- Coachella!!

We caught up with the F&F Entertainment rookie group -- formed via the SBS competition show, "Universe League" -- ahead of their debut ... and they shed some light on the whole process and what they learned about each other along the way.

All nine members (Steven, Jeongwoo, Woongki, Shuaibo, Han, JL, Juwon, Chih En and Daisuke) peeled back the curtain on topics like their influences, dream collabs (hi, Sabrina Carpenter), and what makes them so unique ... which fittingly ties into the title of their mini album, "WHO WE ARE."

The Ying Yang Twins recently got LOWWWWWWW for a viral performance at SeaWorld that had social media wondering how so many colorful words were allowed in the family-friendly theme park ... the answer being, the PARENTS KNEW ALL THE DIRTY LYRICS!!!

TMZ Hip Hop caught up with D-Roc and Caine and the Atlanta rap legends urge everyone to go back and re-watch and tune out the San Diego crowd.

They're adamant they didn't cuss -- not one, damn time!!!

Halle Bailey found the perfect way to relax in Italy after her grueling custody battle with her ex, DDG -- with the company of a new beau while her buns baked in the sun!!!

"The Little Mermaid" actress was in Positano, Italy, on Saturday, where she and her mystery man were spotted splashing, kissing and cuddling under the Mediterranean Sea.

Halle looked happy posing her bikini bottom for her chocolate, dreadhead man -- but couldn't prevent her thong, th-thong, thong, thong going up the wrong, wr-wrong, wrong, wrong way!!!

Ja Rule recently made 50 Cent the target of ridicule with claims his longtime rival had a paltry crowd turnout at his recent Euro tour stop ... a misfire diss, because we've obtained proof the show was actually at capacity!!!

50 Cent was live inside Hannover, Germany's Heinz-von-Heiden-Arena for his "Legacy" tour on June 28 ... a show where he sold more than 25,000 tickets.

A representative for Curtis “50 Cent” Jackson provided ticketing info and tells TMZ Hip Hop, “Like all of Jackson’s other tour dates, this show was completely sold-out.”

Lizzo just got brutally honest about the hell she’s been through -- from the bombshell lawsuit to harassment claims -- admitting she hit such a dark place, she seriously considered giving up on life.

The singer didn’t sugarcoat a thing in Women’s Health -- dropping the chilling question, "You ever get tired of living?" before revealing the pain ran so deep, she found herself thinking, "I could die."

Lizzo clarified she never tried to end her life before -- or even planned to -- but the hate got so loud, she started to wonder ... If everyone thinks I’m this awful person, then what’s the point of being here at all?

It's the second day of jury deliberations in the Sean "Diddy" Combs federal sex trafficking and racketeering trial in NYC Tuesday, and arguments over a late-afternoon note sent to the judge Monday shed some light on the opposing legal teams' strategies.

Jurors sent a note to Judge Arun Subramanian asking ... "If an individual asks for a controlled substance and the person hands it over, it is distribution?"

In the back-and-forth in the courtroom, the prosecution team wanted a clear "yes" answer to the question. The defense team simply wanted a restatement of the judge's original instructions ... which seems to indicate they wanted the jury to continue to wrestle with the issue because the jury presumably already had the instructions packet when they sent the note to the judge.

You can bet Katy Perry kissed the ground after escaping this latest stunt… 'cause the pop princess got straight up trapped mid-air in a giant hamster ball!

It all went down Sunday night during her "Lifetimes" tour stop in Adelaide, Australia ... when the giant metal sphere meant to lift Katy above the crowd suddenly tilted -- sending her clutching the frame for dear life to keep from toppling out.

As you can see, Katy was really putting that upper body to work, clinging on for dear life -- and to make it all even scarier, the music cut out and the lights dimmed as crew scrambled to step in.

Orlando Bloom's got Buddha on his brain following his split from Katy Perry ... taking to Instagram to post a cryptic quote about new beginnings from the spiritual teacher.

Check out the actor's Monday post --  he seems to be doing some serious reflecting by sharing Buddha's saying ... "Each day is a new beginning. What we do today is what matters most."

But he didn't stop there -- Orlando took to his story to share a message from Japanese author Daisaku Ikeda that reads ... "The important thing is to take that first step ... Bravely overcoming one small fear gives you the courage to take on the next."

Put those "2 Hands" on Tate Mcrae's sexy snaps to kick off her 22nd birthday! After all, what better way to celebrate another year around the sun than goin' for a sexy scroll through Tate's hottest bikinis and dance 'fits ...

Legs for days, the singer-dancer -- whose fame first stemmed from competing on "So You Think You Can Dance" -- choreographed this long n' lean, boat babe selfie in a white-hot 2-piece!

Earlier this year, the birthday girl dropped her third studio album "So Close To What" -- heating up the music charts with hit songs like "Revolving Door," not to mention her music video dances goin' viral on social media.

"It's okay, you're okay" ... Hit up our gallery and send this Canadian beauty your well wishes!

Rumors have been circulating that Lady Gaga and Elton John both demanded a huge pile of money to perform at the wedding of Jeff Bezos and Lauren Sanchez ... but TMZ has learned it's all BS.

Here's the deal ... with the Venice mega-wedding in the rearview mirror, gossip has been spun into headlines -- such as both superstars wanting a fee of $6 million apiece to perform for the 200 who's who guest list -- which Bezos passed on.

Insiders for both icons tell TMZ ... the whole story is laughable ... 'cause it just didn't happen. We hear that neither Elton nor Gaga was even approached to play the wedding -- let alone demand such a gigantic fee.

Hours after jury deliberations in Diddy's federal trial hit a bump when the jury foreperson sent a note about Juror No. 25 being unable to follow instructions ... a second communication from the jury room was sent to the judge.

Just around 4:50 PM ET Monday, Diddy was brought back into the courtroom by federal marshals ... Judge Arun Subramanian announced he'd received two new notes from the jury.

The first note sought clarification on the racketeering-related count -- "If an individual asks for a controlled substance and the person hands it over, it is distribution?" The defense and prosecution attorneys both told the judge they wanted to weigh in on this note.

Loads of Diddy clips and soundbites have been subject to social media scrutiny since his federal sex trafficking and racketeering trial kicked off -- but probably none bigger than his infamous "Drink Champs" interview with Fabolous and Jadakiss!!!

N.O.R.E. hit "The Breakfast Club" on Monday to clear up the viral fiasco where Diddy made some eyebrow-raising comments towards the star NYC MCs ... something about "loving when they're scraping and scrambling for sh*t."

The clip occurred nearly 8 years ago, and N.O.R.E. says he's still getting tagged in it to this day -- but says there's a perfectly good explanation for the shenanigans!!!

Post Malone is back on the market -- because he's no longer in a relationship with Christy Lee ... TMZ has learned.

Sources with direct knowledge tell TMZ ... the former couple called it quits a little under a month ago after being together romantically since the start of the year. It's unclear whether the pair remains on friendly terms.

The couple was first spotted together in January during a dinner outing in Rome.

"It's Cowgirl Lizzo reporting for duty!!!"

Singer Lizzo delivered quite the show with a head-to-toe denim look -- showcasing her curves in a plunging zip-up top paired with some daisy-dukes ... Yeehaw!

The all-star look -- which debuted on the star's Instagram -- was graffiti-ed with "Cowgirl Lizzo" on the front and "hoe" on her backside.