Cash App founder Bob Lee was allegedly a regular at underground sex and drug parties with other San Francisco elites — including the sister of the man accused of killing him, according to a new Wall Street Journal report

Lee's stabbing death on April 4 was originally thought to have been the result of random violence in the crime-ridden city.

But friends of the tech mogul now say it was the result of Lee's partying with Khazar Momeni, the 37-year-old wife of a prominent plastic surgeon and the sister of Nima Momeni — who has been charged in his death.

Khazar and Lee were in a relationship in the weeks leading up to his death in early April, his friends told the Wall Street Journal, and many feared he had fallen into a dangerous lifestyle, surrounding himself with the wrong group of people.

Prosecutors have previously said Momeni stabbed Lee in the heart multiple times after vowing to 'come down hard on him' and grilling him over his relationship with Khazar, with whom the Cash App founder exchanged intimate text messages.