“Real Housewife” Luann de Lesseps drunkenly took over the mic at a gay piano bar, belting out tunes, telling booing patrons “f–k you,” and was eventually kicked out, though she denies she was given the boot.

Of “The Countess” — who has publicly battled with sobriety — a source said, “She monopolized the piano, but that isn’t how it works, you sing [one song] and move on.”

The 56-year-old reality star, who performs her own “Countess Cabaret” show, already seemed sozzled when she showed up at the piano bar Townhouse in Manhattan on Wednesday night, witnesses said.

She grabbed the mic and simply wouldn’t stop, said the source, “Luann thought she was doing her act. She tried to sing [her own song] ‘Money Can’t Buy You Class,’ but they didn’t know it, they know standards.”

“The piano player was like, ‘I don’t know the song,’ and she responded ‘It’s a hit!’” The critically-trashed song apparently sold 19,000 digital copies.

Of her 2010 autotuned debut single that includes lines like “Elegance is learned,” the snarky source sniffed, “It’s not a Cole Porter standard, it’s not ‘Somewhere Over the Rainbow.’”

Undeterred, a liquored-up de Lesseps kept “belting out jumbled versions of songs,” which were so intolerable, “the crowd began booing her,” in front of stunned drag queens including Tiffany Anne Coke, Shiny Penny, Lauren Ordair and Chandilier, says another source.

Things took a turn for the worse, when Luann began “yelling at the gays, ‘You don’t know me! I’m a cabaret star!’” added one source.

Video taken by a patron, seen by Page Six, shows de Lesseps — in a considerably crude un-Countess like move — snarling at the crowd “F–k you,” while on the mic singing.

The tipster tells us that de Lesseps “yelled at the other patrons on the microphone,” and then was “thrown out for getting aggressive with the bar’s customers.”

A [probably very hungover] de Lesseps explained to Page Six on Thursday through an intermediary, “I was at rehearsals all day yesterday [for her upcoming cabaret show at Feinstein’s/54 Below], then went to dinner with Broadway producers. We were in a celebratory mood and drinking champagne.”

She says that she then went to Townhouse with Tony Award-winning “Kinky Boots,” producer Jim Kierstead at around 10:30 PM and “there were a bunch of people singing and it was a fun, boisterous crowd.” Kierstead suggested she sing a few songs.

“I got up and sang a few Broadway songs they were playing,” she says. “I realize I was a little bit tipsy, but we were having fun and it was getting late. I’d been rehearsing and I was in the mood to sing a few songs. Then Jim said to me, ‘Lu, I have an early rehearsal,” and then we left around midnight, 11:30 PM.”

According to Kierstead, “After a birthday party for a NY theatre personality, Luann and I went to the Townhouse for a nightcap. She was met by legions of her fans and was convinced to sing for them.

“I was finally able to bring her home as I had an early morning Thursday for the workshop of a new musical. Of course she was the belle of the ball as usual.”

A friend of de Lesseps added that when it comes to staying on the wagon she has been “trying to stay healthy and takes things day by day.”

De Lesseps was previously arrested in 2017 in Palm Beach on Christmas Eve for being drunk and disorderly, allegedly kicking a police officer and yelling, “I am going to kill you all.”

She agreed to plead guilty to battery, trespassing and disorderly intoxication in exchange for the felony charge against her being reduced.

De Lesseps was ordered to perform 50 hours of community service (with at least 10 hours per month) and attend two Alcoholics Anonymous meetings a week in New York, per the deal.

She then went to rehab and has continued having extra help with her sobriety over the years.

Unfortunately, in December, de Lesseps launched a non alcoholic-rosé, Fosé Rosé, which she is currently promoting — but clearly not drinking.

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