A glamorous fashion designer found dead under mysterious circumstances at an upscale Montauk yacht club was bloodied, with the scene wiped clean before cops got there, a lawyer for her family said.

The bombshell revelations cast more doubt that 33-year-old Martha Nolan-O’Slatarra died from a drug overdose aboard a yacht called “Ripple” at the ritzy club on Aug. 5, 2025, as cops initially believed, according to attorney Michael Bowe of Brithem LLP.

“Our investigation included a second autopsy by world renowned medical examiner who does not believe Martha died from intoxicants, especially given her youth and good health and there are facts we will present and expect to develop that we believe will show otherwise,” Bowe told The Post.

“For now, I will share that the EMT’s found blood in her mouth, on her chest and head and possibly behind her head; law enforcement informed the family they believed the scene had been cleaned before responders arrived,” the lawyer said.

Bowe on Tuesday filed a “notice of claim” announcing the family’s intention to file a $50 million wrongful death suit in Manhattan civil court against the boat’s owner, Christopher Durnan, arguing that Nolan-O’Slatarra died due to assault and negligence, not an overdose.

The notice does not detail specific accusations against Durnan, but claims he “intentionally and wrongfully assaulted” Nolan-O’Slatarra.

Durnan, who could not be reached for comment, has never been charged in the case.

Nolan-O’Slatarra, an Irish-born beauty, launched a swimwear fashion company in the Hamptons, East x East, in which Durnan, an insurance mogul, had invested.

The two were reportedly discussing business when tragedy struck.

Her family maintains that Nolan-O’Slatarra only had “trace amounts of cocaine” in her system — not enough to trigger a lethal overdose.

Independent autopsies also found no evidence that the dead woman had vomited before she died, dashing claims allegedly made by Durnin that he stripped off his clothes because she had thrown up on him, Bowe said.

But one year later, the case remains under investigation, and Suffolk County cops have been slow to provide answers — the department has denied multiple freedom of information requests from The Post for autopsy results and other documents tied to Nolan-O’Slatarra’s death.