Luann, don’t be uncool.

An insider tells Page Six that Luann de Lesseps stormed out of the Broadway opening night of “Bad Cinderella” when she realized she had been seated near former “Real Housewives of New York” castmate Bethenny Frankel.

De Lesseps, 57, came to the Andrew Lloyd Webber musical with her former boyfriend Jacques Azoulay and arrived at 6.30 p.m., just as the curtain was about to go up.

Originally the show’s publicist, Rick Miramontez, had seated the former castmates right next to each other until another member of his team advised him that the seating arrangement was not a good idea.

They were then split up, with Bethenny and her date, 12-year-old daughter Bryn Hoppy, seated directly across the aisle from de Lesseps.

“I am not well versed in the ways of ‘Housewives’ and should have known better than to seat them so close to each other if indeed it was a politically incorrect move,” an apologetic Miramontez told Page Six. “Next time I’ll do my homework.”

Unfortunately, the seat wasn’t far enough away for the “Feelin’ Jovani” chanteuse.

The insider says that during intermission, de Lesseps spied Frankel, 52, and “the next thing I know is Luann grabs Jacques’ arm and storms up the aisle.”

“She looked visibly upset and they left in a huff,” the source added before noting that no words were exchanged between the Bravo alums, “just a look.”

Frankel, who clearly was wearing her big-girl panties, stayed for the second act of “Bad Cinderella” and gave the show a rave on social media calling it “f–king fun” and “fabulous.”

And Miramontez has graciously offered de Lesseps another chance to see the show — presumably sitting nowhere near Frankel.

“Whenever Ms. de Lesseps wishes to come back, she’ll be our guest,” he told Page Six, “and we thank Bethenny for her words of praise for the show.”

Frankel’s rep declined to comment and de Lesseps’ rep replied with a cryptic comment.

“‘Bad Cinderella’ was not the only one feeling bad, that’s why I left with my date,” she said.

The two, who were in the original cast of the reality show when it premiered in 2008, have long had a documented history of ill will.

When Frankel first left the show in 2019, de Lesseps voiced her happiness over the departure.

“I think the whole cast is relieved in a way,” she said on SiriusXM’s “The Jenny McCarthy Show.” “It also leaves breathing room for other women to shine and show their personalities because a lot was Bethenny coming in and stealing the show.”

De Lesseps also dissed Frankel’s Skinny Girl brand.

“God, if I had a dime for every Skinny Girl party I had to promote, and then she can’t even promote my cabaret show and be happy about it,” she groused.

Even last year, de Lesseps slammed Frankel for launching a “Real Housewives” rewatch podcast.

Appearing on an episode of “Everything Iconic,” de Lesseps agreed with host Danny Pellegrino that Frankel has spent the majority of her years away from “RHONY” “sh–ting on the show.”

“Right, and if she s–ts on the show, that means she’s gonna s–t on us on her little podcast about the ‘Housewives,’” the mother-of-two predicted.