Luann’s big B’way blunder

IT’S the ol’ razzle-baffle. After reality star and cabaret singer Luann de Lesseps triumphantly announced Thursday night that she’ll be appearing in “Chicago” on Broadway, reps for the star tell us that she is sadly mistaken.

While her “Real Housewives of New York City” co-stars were casting doubt on her singing chops during the Bravo series’ recent reunion show, de Lesseps chided them, “I want to tell you all right now, that for someone who can’t sing, I just got cast in ‘ Chicago’ on Broadway.”

But on Friday her own rep told us she’d jumped the gun: “Due to scheduling conflicts — between her [Bravo show], her jewelry line and her successful cabaret tour [‘Countess and Friends’] — Luann will not be joining the cast of ‘Chicago’ at this time.”

De Lesseps — who has been trying to land a role in the long-running musical for nearly a decade now — had been telling pals as far back as six weeks ago that she’d been cast as the show’s warden character, Mama Morton.

A source told Page Six that the production had been in talks with de Lesseps, but ultimately decided to go in a different direction.

De Lesseps has had a recent run of unpredictable behavior. Over the past two years, she’s been arrested for a drunken rampage, then taken into custody for allegedly violating her parole, and she’s gone to rehab twice.

When Page Six contacted the Broadway show weeks ago about the scuttlebutt that she was being cast, reps for the show told us there were no plans for her to appear. A production spokesperson said in June, “Luann de Lesseps is not confirmed to join the cast of ‘Chicago’ at this time.” Apparently, de Lesseps didn’t get the memo?

A source said that de Lesseps made the announcement on the reunion spontaneously, perhaps because she was feeling defensive while under attack from her fellow “Housewives.”