Beyonce & Jay-Z

The reality TV star accused of having an affair with Jay Z is flat out denying she ever had sex with Beyonce's man ... and now she's gearing up for a legal battle.

Casey Cohen -- who was on the Bravo show "Princesses: Long Island" -- was named as Jay's alleged side piece in several magazines (such as In Touch) ... all owned by Bauer Media Group.

TMZ has learned Cohen has hired a lawyer who fired off a cease and desist letter saying Cohen and Jay Z "have never been in love or intimate" -- and dismissing all the Bauer articles as "a foul and phony mistress-rumor."

Cohen cops to having met Jay Z and Beyonce several times -- in the letter, obtained by TMZ -- but only through her job working as a VIP hostess in New York City.

She is demanding Bauer issue a public apology to her, Jay Z, and Beyonce ... and remove all posts about her from the Internet.

Beyonce and Solange's reunion in New Orleans really was a family affair ... TMZ has learned Jay Z also joined in on the fun.

Bey, Solo and Hova all hit up New Orleans hot spot Cafe Amelie for more than 2 hours Saturday ... according to multiple sources -- and the fam came with a MASSIVE security detail and 3 black SUV's waiting nearby.

We're told a team of bodyguards waited outside making sure no one could get a clear shot of the threesome hanging out.

The person who snapped this pic says when it came time to leave, Jay and Beyonce darted in separate directions to the car ... forcing the photog to choose one. The queen won.

Beyonce later posted a family picture from the lunch ... Jay Z, Solange, and all.

Beyonce is putting it out there as clearly as she can ... she's a member of one big happy family.

Beyonce and Solange reunited in New Orleans Saturday ... Bey posted a pic of the two embracing on Instagram -- and captioned the date and location to show it was legit.

No sign of Jay Z.

Until 4 hours later ... when she posted the trailer for her upcoming collab with Hova and a ton of celebs called "Run."

They are indeed ... just like us.

Jay Z and Solange are finally addressing the infamous elevator fight video ... saying BOTH sides are to blame for the violence that unfolded.

Jay Z, Solange, and Beyonce released the joint statement moments ago, saying, "Jay and Solange each assume their share of responsibility for what has occurred. They both acknowledge their role in this private matter that has played out in the public. They both have apologized to each other and we have moved forward as a united family."

The statement continues, "The reports of Solange being intoxicated or displaying erratic behavior throughout that evening are simply false. At the end of the day families have problems and we're no different."

"We love each other and above all we are family. We've put this behind us and hope everyone else will do the same."

The statement still doesn't explain what caused the fight, but Jay and Solange say they have worked through it.

7:10 AM PT -- Solange's rep says she wasn't in NYC. However, we were told by Mr. Flawless himself that he personally waited on Jay Z and Solange ... and was specific as to how long they were there and where they were looking inside the store.

We also spoke with a famous NYC DJ who happened to be outside the store, and also insists he saw Jay Z and Solange come out of the store, get into a Mercedes-Benz G Wagon and drive off.

Jay Z and Solange Knowles went looking for jewelry together Tuesday afternoon at a high-end NYC jewelry store ... TMZ has learned.

Our sources connected with the store say Jay and Solange were in Mr. Flawless, where they were looking for women's jewelry for around 20 minutes.

We're told the pair showed no signs of strife, and looked at gems with Mr. Flawless himself. They looked, but tried nothing on. They left the store without buying anything.

Jay and Solange didn't talk much inside the store ... they pretty much just browsed quietly.

If a picture says a thousand words, what do four pictures say?

In the first "response" of any kind since the blowout fight between Solange and Jay Z, Beyonce posted four photos of her with her sister to her Instagram page early Wednesday morning.

Only one of the photos was captioned and it merely said, "good morning."

It's curious ... since Beyonce merely stood by and watched Solange go ballistic on Jay Z. Is she saying she's taking Solange's side in all this? Is she saying she supports her sister despite her being completely in the wrong?

The first couple of hip hop made their mark on Coachella Saturday ... surprising two different audiences with unannounced appearances -- and the hipsters went BONKERS!

First up, Beyonce ... who danced her way onto the stage during little sister Solange's set. However Queen Bey didn't grace the Indio crowd with a single note.

Next, Jay Z ... who rapped alongside his former nemesis Nas for a few minutes -- then made his swift exit from the festival.

To the victor go the spoils ... just ask Russell Wilson, who's sitting courtside at the Brooklyn Nets game with Beyonce and Jay Z.

Call her Bouncé ... because Queen B advertised more breast last night than Popeyes.

Beyoncé was showing off the girls at Hennessy's Super Bowl afterparty in NYC, wearing a v-neck t-shirt that was so deep it was poetic. She and the twins got their groove on while Nas and Kelly Rowland performed on stage.

Proud husband Jay Z was there too ... but we all know what the real attraction was.

Beyonce -- last year's Super Bowl performer -- surprised the crowd at Jay Z's concert last night in New York ... when she hit the stage to jam out with her husband on their latest song.

The whole thing went down at DirectTV's "Super Saturday Night" party on the eve of the big game -- and last year's halftime entertainer pulled off the surprise performance without a hitch.

The halftime show this year will be put on by Bruno Mars and the Red Hot Chili Peppers.

Beyonce and Jay Z celebrated Blue Ivy's 2nd birthday in spectacular fashion ... closing down an entire theme park -- for a celebration that the kid will never remember.

Blue Ivy spent the day Tuesday with lemurs, orangutans, kangaroos and penguins at Jungle Island -- a wildlife park and botanical garden in Miami.

Park officials are keeping the cost under wraps ... but it's gotta be pricey to close the entire park. Put it this way ... a VIP safari tour for just one person costs $240.

Beyonce's favorite thing to do these days is to post photo evidence she's not pregnant ... which reminds absolutely no one -- have ya seen "Black Baby?"

Hey, you asked for it.

Touring is tough, and Beyonce's figure out a way to keep the heat on ... in a good way.

B posted a photo of herself with her only child, Blue Ivy, relaxing in a jacuzzi.

It's clear from the photo, mother and daughter are crazy in love.

Crazy week for celebrities ... and speaking of crazy, we gotta ask ...

Rather than simply come out and say "I am not pregnant" ... Beyonce chose to deflect the rumors once again ... this time by posting a photo of her drinking a glass of wine with hubby Jay-Z.

Rumors of Bey being knocked up have been swirling for weeks, beginning when she canceled a concert in Belgium and cited the dreaded "exhaustion and dehydration."

She also posted (and quickly deleted) a diatribe on Instagram slamming the rumors ... but at no point has she ever denied them.

This photo doesn't put the rumors to rest either ... doctors aren't completely against a pregnant woman having a glass of wine every now and again. So we ask ...