Diana Jenkins has long been dogged by allegations she runs a prostitution ring, but she says it's BS and she's finally battening down by threatening legal action to clear her name.

We've learned the entrepreneur and philanthropist -- who was just added to the "Real Housewives of Beverly Hills" cast -- fired off 8 cease and desist letters to multiple parties she says continue to perpetuate this nasty lie about her.

TMZ has obtained those letters, drafted by her attorney, J. Erik Connolly, who makes her demands crystal clear ... stop the false statements, correct the record, and apologize.

We're told there are several bloggers and publications Diana is going after -- but 2 of the big fish she says bear most of the responsibility for ruining her rep are the magazine Jezebel, and a social media personality known as "Enty Lawyer."

Enty is an anonymous account run by someone purporting to be plugged into showbiz with inside knowledge. In Diana's scathing C&D, however, she says Enty Lawyer has anything but.

The attorneys write, "You have put yourself in a precarious and potentially ruinous position. Perhaps you believe that a 'get out of jail' card exists if you can persuade a court or jury that your statements about Ms. Jenkins and her companies are 'pure opinion.'"

They add, "That is not going to happen. You have held yourself out as someone that your audience can and should rely upon for uncovering facts. That is how you have built a following and a brand. That is why you have used the term 'lawyer' as part of your handle. You do not promote yourself as a purveyor of 'make believe.' You have branded yourself as something else for purposes of self-promotion and enrichment. Those facts foreclose the 'pure opinion' defense."

Enty has also suggested Diana has deep ties to the late Jeffrey Epstein, who was accused of sex trafficking by multiple women. Diana believes this all stems from something infamous she wrote in 2009 -- a coffee table book called "Room 23," featuring raunchy pics of models/celebs.

Since its publication -- not to mention a follow-up Jezebel article in '12 -- rumors had swirled about Diana's alleged involvement in Hollywood pimping at the highest levels ... and now that she's on 'RHOBH,' they have fired up anew.

We should note ... Diana has vehemently denied outright that she's ever been involved in anything like that whatsoever, and is once again reaffirming that in these letters.

Speaking of Jezebel, the C&D sent to them is quite forceful as well. Referencing 2012 and 2022 articles, Diana's team says ... "Beyond the obvious legal issues, what you have done to Ms. Jenkins is simply wrong. She is a mother, a philanthropist, and an entrepreneur. Her philanthropic endeavors are well known and have generated millions of dollars in assistance for victims of human rights violations, natural disasters, wars, and health epidemics. To characterize Ms. Jenkins as a prostitute, sex trafficker, and criminal is not just factually inaccurate, but sexist."

Diana hasn't actually filed any lawsuits just yet, but it sounds like she's strongly considering it if any of these entities don't change their tune and issue retractions.