Lisa Rinna, 54, Poses In Tiny Strapless Black Bikini From Dorit Kemsley's Swimwear Line

Lisa Rinna is flaunting her bikini body again. However, the 54-year-old actress isn't just strutting around in a skimpy swimsuit to show off her tiny waistline and toned physique; she's doing it to help her Real Housewives Of Beverly Hills costar Dorit Kemsley promote her new beachwear line, Beverly Beach by Dorit.

On Friday, Rinna took to Instagram to prove that purveyors of swimwear don't need to hire models in their 20's to sell bikinis. In the mirror selfie that she shared with her followers, Rinna is rocking a black strapless bikini with low-cut bottoms. The top features knot detailing and a cutout strategically placed between the breasts, or a "cleavage window."

Rinna accessorized her bikini with a floppy black hat and a pair of over-sized shades. She didn't share any details about her swimsuit with her followers, simply captioning her photo with a taco emoji and the word "OLÈ."

Her two-piece is from the Beverly Beach by Dorit swimsuit line, and the Instagram account for the brand turned Rinna's selfie into an ad by re-posting it. As reported by 2Paragraphs, Dorit Kemsley said that she has named some of her bikinis after her Real Housewives of Beverly Hills costars. However, the bikini Lisa Rinna is rocking in the snapshot below is called the "Amanda."

"WHAT A BABE @lisarinna looking hot af in the Amanda bikini #beverlybeachbabe #bodygoals #slay #yaasss," read the post on the beachwear brand's Instagram page.

For the record, the "Lisa" is also a black two-piece. However, it features a classic string bikini design with bottoms that tie on the sides and a top with halter straps.

During a recent interview with Entertainment Tonight, Kemsley chatted about her new beachwear line, which recently got plenty of free publicity when its launch was turned into a Real Housewives Of Beverly Hills storyline. As reported by Entertainment Weekly, some major drama went down at the launch party, and the end result of an argument about heads being chopped off in pictures and another rehashing of "panty-gate," with Kyle Richards storming out of the event. Luckily, Dorit did not go into the bikini business with any of her female castmates. Instead, she's working with her husband, PK.

"I'm so grateful to have his expertise and his advice, and to have his shoulder," Dorit said. "I think it works. I love having him a part of the business. I did it for many years without him, and I was successful at it, so it's not a matter of whether I can or cannot do it. I just feel like it's just better having him along for the ride."

The three-part Real Housewives Of Beverly Hills reunion special begins airing Tuesday, April 24, at 9 p.m. ET on Bravo.