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Leonardo DiCaprio had either the best night of his life or a super awkward encounter with former GF Rihanna and new rumored fling Nina Agdal ... both under the same roof at the same time.

The three partied at Up & Down club in NYC Tuesday night as RiRi looked awesome, paying homage to Nine Inch Nails. Meantime ... Leo had his hands full trying to go incognito with the S.I. cover model.

Bill Cosby has been ordered to stand trial for allegedly sexually assaulting a woman.

A Pennsylvania judge just ruled, there is probable cause to believe the comedian drugged Andrea Constand at his Philadelphia mansion back in 2004 and stuck his hand down her pants and fondled her.

Cosby faces up to 10 years in prison if convicted of aggravated indecent assault.

He'll be arraigned in July.

Kelly Rohrbach is totally comfortable in that classic "Baywatch" one-piece, and just as comfortable out of it ... based on the nip slipping that went down during a photo shoot.

Kelly was posing Monday in Malibu for a Vogue spread that looked like a big promotion for the "Baywatch" movie -- and also for her amazing body.

Prince Harry took the same dive at Disney World he took 23 years ago with his mother, Princess Diana.

Harry was screaming through the big drop on Splash Mountain last week in Orlando ... and, no doubt, reminiscing about his 1993 visit to the park with Di and his big bro William.

They grow up so fast ...

Kim Kardashian was in full formal camouflage Monday night, fully fit for a Vogue shindig.

Kim and Kanye flew from Rome to London for the event, where the British version of the mag is celebrating its 100th birthday.

Lady Gaga found a ride more eco-friendly than a Prius on her way to grab a smoothie in Malibu.

Gaga ditched 4 wheels for her 4 legged white horse, a gift she got last Christmas from her music label, Interscope.

Eva Longoria's nuptials to Mexican media mogul Jose Baston was no shotgun wedding ... but it was stocked with plenty of semi-automatic assault rifles.

Eva and Jose got married Saturday, about 90 minutes outside of Mexico City ... and anyone trying to get into the party without an invitation had to go through a wall of guys with military grade weapons.

It's the kinda protection you'd expect for a politician or someone as powerful as Jose -- who is the president of Televisa, one of Mexico's biggest media companies.

Not to mention, the high-profile guests like Victoria and David Beckham.

Mazel.

Kim Kardashian narrowly avoided a huge wardrobe malfunction while out to dinner and the opera Sunday night with Kanye in Rome.

The two are in Italy celebrating their 2nd wedding anniversary, which is Tuesday, and Kim definitely knew how to make sure her husband's eyes were glued to her. Same holds true for every other guy within a 50 foot radius.

Wheeeen the boob hits your eye like a big pizza pie ... that's amore.

Ciara chic is awesome ... a blend of a sexy physique, amazing threads and super expensive shoes, which is evident from the price tag.

We're guessing this isn't a humble brag ... just an oversight.

Oops.

Fresh off his Mexican vacation, Louis Tomlinson got a fresh dose of reality when baby mama Briana Jungwirth handed over their 4-month-old son Freddie.

Looks like Louis is on daddy duty at least through the weekend ... the exchange with Briana went down Thursday afternoon outside a Starbucks in Thousand Oaks.

Louis' rented a home in nearby Calabasas for Briana and Freddie, so it's unclear why they'd make the exchange in a parking lot ... then again, when you're raising a little tyke, got to fit in those Starbucks runs somehow.

Tyga clearly has a type ... his new chick is Kylie Jenner's scrumptious doppelgänger.

The rapper and his rebound, Demi Rose, posed and got cozy in Cannes. Check out the pics ... Tyga likes 'em young. Rose is a 21-year-old British lingerie model.

Speaking of rebounds ... Kylie's also back in the saddle with PartyNextDoor.

#GiddyUp

Gwen Stefani and Gavin Rossdale put their differences aside in the name of basketball ... and co-parenting.

For the first time since their divorce, the exes were seen together Wednesday -- just feet apart -- at their son Kingston's hoops game. There were smiles, from Gavin at least, but they were hardly chummy. More like cordial.

Exes playing nice ... it's catching on.

He's out of the NFL, but ex-NY Jets safety Kerry Rhodes is still in game day shape -- and flexed his physique this week during some beach football with his actress fiancee.

BTW, Rhodes is engaged to actress Nicky Whelan -- the hot chick Owen Wilson almost banged in "Hall Pass."

Two paths diverged for Leonardo DiCaprio on a dance floor in Cannes and Leo took the road less traveled.

Leo had a gorgeous blonde to his right and equally stunning brunette to his left -- in his world ... a typical Tuesday night. His track record with blondes (especially models) is legendary, but this time he thought ... what can brown do for me?

Turns out the dark-haired mystery chick is Georgia Fowler ... Harry Styles' ex ... who is a model, so Leo wasn't straying too far when the pair got cozy.

Turns out you can travel both roads.

Kristen Stewart hit up the Cannes Film Festival Tuesday night ... camera ready for a 'Twilight' sequel.

Sorry Twi-hards, no Edward and Bella reunion. K-Stew threw on some serious dark shadows for the premiere of her indie flick "Personal Shopper," which happens to be a ghost story, so she was right on the money.