The Real Housewives of Orange County stars Vicki Gunvalson and Brooks Ayers have been involved in shady dealings before, but nothing like this.

He is accused of trying to orchestrate a murder-for-hire plot against their associate, sensational court papers filed in Las Vegas, Nev., charge.

Ayers has filed a slander and defamation lawsuit against Gunvalson’s ex-business partner, who he claims went public withthe false allegations.

Robert Williamson III says Ayers planned to have him killed.

This is how the stunning situation supposedly went down:

WIlliamson pressured Gunvalson into attending a secret meeting at the Bellagio Hotel in Las Vegas in March when she was in town for Ayers’ birthday.

Surrounded by “bodyguards,” Williamson, his wife, Cate and another associate began to air his disturbing claims against Ayers, the lawsuit alleges.

Incredibly, they told her Ayers was a “dangerous guy who has threatened Plaintiff (Williamson) and his wife’s life” and that he “hired a hit man to kill plaintiff.”

According to the suit, they also claimed Ayers got the paralegal from his divorce attorney in Mississippi pregnant, causing her to lose her job.

Moreover, he conspired with another person to extort money from Williamson and that Ayers had “many” sexual diseases. Ayers denies all the allegations.

Vicki Gunvalson, 51, believed the claims at first, it’s claimed, even sending her lover a message telling him to “lose [her] number" ... then changed her mind.

Ayers says after she realized the claims were bogus, they got back together. Now Brooks is suing for damages, claiming that he “was publicly vilified."

He says he is entitled to "substantial damages in the form of pain, suffering, anguish and lost business opportunities” because of the accusations.

Williamson is already suing Ayers, claiming he committed fraud, breached contract, failed to live up to good faith dealings, misrepresented himself and more.

The former business associate says Ayers conspired with Gunvalson to unjustly enrich themselves while working with him to launch her vodka line.

He is also planning to re-file his own lawsuit against The Real Housewives of Orange County star herself, after settlement talks collapsed this summer.

Oh, and he is also accused of calling Vicki a “f*cking whore” on tape ... and threatening to “beat her ass,” and bragging that he’s free with his hands.

“Because," he proclaims, "that’s what we do in the South.”

You gotta hear this ...