Diddy’s Ex-Assistant Claims Mogul Threatened to Kill Kid Cudi Over Cassie Romance

Capricorn Clark, a former Diddy employee, continued her testimony in the disgraced rap mogul's federal racketeering and sex trafficking trial Tuesday, revealing more details about Diddy's discovery of the relationship between Cassie and Kid Cudi ... including a menacing threat.

Clark said Cassie would sometimes stay with her at her apartment in L.A., and she said Cassie once brought Kid Cudi there. She described a text about Cudi she says she got from Cassie, and she told Cassie to delete the text because Diddy was paying for both their phones. She said she took Cassie to get a "burner" phone.

Clark testified early on the morning of December 22, 2011, Diddy was outside banging on her front door ... she says she opened the door to find him holding a gun, and asking her, "Why didn't you tell me? Who is Scott?" Kid Cudi's legal name is Scott Mescudi. She said she didn't know anyone named Scott.

Clark testified Diddy said, "We're going to kill this n****." She described accompanying Diddy in a black Cadillac Escalade, with a bodyguard. Diddy got in the back with her, and he had a gun in his lap, according to Clark.

She said they drove to Cudi's house in the Hollywood Hills, about 15-20 minutes away ... she said Diddy and the bodyguard Ruben went into Cudi's house.

Clark said she called Cassie on Cassie's burner phone, then changed the name on her phone to someone else ... but Diddy allegedly grabbed her phone and dialed the last number called. At that point, she says Cudi himself drove up, and Diddy recognized him. She said they drove off, and they saw police approaching Cudi's house.

Clark said Diddy told her to convince Cudi not to tell police it was Diddy at his house. She then picked up Cassie, and they went to Cudi's house to try to get him not to file a police report, telling him Diddy had been there with a gun. CC's message to Cudi, "If you tell on him, he'll hurt us all."

Back at Diddy's house, Clark testified, Diddy kicked Cassie repeatedly. She says Cassie was curled up in the fetal position, and Diddy kept kicking her "all the way to the street." She testified she called one of Diddy's bodyguards to try to get him to stop attacking Cassie ... she was told to leave. She said she called Regina Ventura, Cassie's mother, telling her Cassie was being assaulted and that she couldn't call police, but Regina should.

Clark was also asked by the prosecution about an email ... Clark said it was from Cassie, saying Diddy threatened to release sex tapes of her, and saying Cassie and Cudi were threatened with harm.

She also said arson investigators reached out to her because Cudi had given them her number. Clark told the jury Diddy had threatened her about 50 times.

She said she was fired in a termination letter for not properly asking for the vacation she had taken.