10/2 -- We've obtained docs that show Horne was more than "merely a vendor" in the company. Horne actually filed a trademark for Beverly Beach back in 2017.

'Real Housewives of Beverly Hills' star Dorit Kemsley says the guy claiming she and her husband screwed him over when they launched her swimwear brand is full of it, and in fact ... it's quite the opposite.

We broke the story ... Ryan Horne sued Dorit and her husband, Paul Kemsley, last month, claiming he struck a deal with them in 2017 to make bathing suits and own a third of the biz. He also claimed he got stiffed out of huge profits.

Dorit's company, Beverly Beach, fired back at Horne with a lawsuit of its own last week. According to the docs ... Dorit is the company's sole owner, and there was never a deal made with Horne for ownership.

BB also claims Horne was "merely a vendor" for the swimwear brand ... but failed to provide the goods and services he promised in a timely or competent manner. The company alleges it was screwed out of hundreds of thousands in lost sales as a result.