Rapper Kid Cudi is testifying at the New York sex trafficking trial of Sean (Diddy) Combs and was expected to testify about his brief relationship 14 years ago with Combs's ex-girlfriend, the R&B singer Cassie.

Cudi, whose legal name is Scott Mescudi, wasn't expected to testify for long, a prosecutor said. The Grammy award-winning rapper, who is known for his alternative hip-hop style, arrived at the courthouse in a black SUV and was escorted inside.

Prosecutor Emily Johnson began her questioning by showing Cudi a photo of Cassie and asking him if he knows her.

"We were friends and we dated briefly," he replied, noting they met in 2008 and recorded some music together, and then dated in 2011.

Asked if he knew who else Cassie was involved with around the time they dated, Cudi replied: Sean Combs.

Cassie testified last week that Combs threatened to blow up Cudi's car and hurt him after he learned she was dating Cudi.

Combs pleads not guilty

Combs, 55, has pleaded not guilty to sex trafficking and racketeering charges after he was arrested in September at a Manhattan hotel. He denies allegations that he used threats and his powerful position in the hip-hop world to abuse women and others, and force Cassie to take part in drug-fuelled sexual performances called "freak-offs" with other men that she said left her too drained to pursue her singing career.

The federal investigation of Combs began in November 2023, a day after Cassie sued him in Manhattan federal court alleging years of sexual and physical abuse. The lawsuit was settled by Combs for $20 million US the next day.

In four days of testimony last week, Cassie, whose legal name is Casandra Ventura, said Combs subjected her to abuse through most of the nearly 11 years she was with him from 2007 through 2018.

She said she developed a relationship with Cudi in late 2011 that she ended within weeks after Combs learned about it when he looked at her phone during a freak-off — one of hundreds she said she endured over the years.

Personal assistant saw Combs become violent

George Kaplan, Combs's personal assistant from 2013 to 2015, testified Thursday that he saw Combs be violent with Cassie only once, on a 2015 trip to Las Vegas aboard Combs's private jet. He said he heard glass breaking behind him and looked over his shoulder to see Combs standing with a whiskey glass in his hand.

"There was tremendous commotion and a scuffle, and then after the glass crashed, Cassie screamed, 'Isn't anybody seeing this?'" Kaplan testified, adding that neither he nor any of the security workers or Bad Boy Records staff on the plane responded to her call for help.

Kaplan said he didn't intervene because he didn't want to lose his dream job. He said he decided to quit after that attack and a later incident in which he saw Cassie sitting in a bedroom with a black eye before Combs sent him to pick up anti-inflammatory medicine at a store to treat the injury.

Kaplan also said he saw Combs become violent with another girlfriend, whom he referred to only as Gina, when the rapper threw green apples at her at his Florida home.

Kaplan told jurors that his tenure with Combs has "proven to be one of the most complicated pieces of my life."

"I'm a young man and this is a god among men talking to me," he said.

Despite seeing Combs abuse Cassie, Kaplan said he still thinks fondly of many aspects of their work together.

Kaplan testified in response to a government subpoena and only after the judge gave him immunity from any potential criminal liability he might face as a result of his testimony.