Sean “Diddy” Combs viciously beat Cassie Ventura’s best friend with a wooden coat hanger to find out if she was cheating on him — and also once tried to bust his then-girlfriend’s door down with a hammer, explosive testimony revealed Monday.

The R&B singer’s former BFF Kerry Morgan recounted a horrific litany of alleged abuse by Combs — including in the aftermath of his infamous 2016 beating of Ventura at a Los Angeles hotel — as she took the stand at his federal sex-trafficking and racketeering trial.

The harrowing testimony in Manhattan federal court revealed Combs’ violence allegedly extended to Morgan — and permanently ruptured her 17-year close friendship with Ventura, whom she said downplayed a nightmarish attack by the Bad Boy Records founder.

Morgan, 39, a model and personal assistant from Buffalo, New York, testified that Combs attacked her “from behind” while she was in Ventura’s apartment in Hollywood Hills in 2018.

Combs “choked me” and left “finger marks on my neck,” before he hit her behind the ear with the hanger, Morgan testified.

“When I got up, he boomeranged a hanger at my head,” she said.

The music mogul wanted to know “who Cassie was cheating on him with,” Morgan said, adding, “I had no idea.”

After, Morgan went to an urgent care facility and was told she had a concussion from the assault. She was dizzy and even threw up a few times from the beating, she claimed.

The attack ended up driving apart Morgan and Ventura, who had been friends since they were teenage models together in New York City in the early 2000s.

Ventura met her bestie at a pizza shop in Hollywood and accused her of “over-exaggerating,” Morgan recalled.

Morgan said she lawyered up and planned to sue after Combs after the hanger attack — but she didn’t end up bringing a civil claim against him because he paid her $30,000.

Ventura had her sign a non-disclosure agreement and that was the last time they ever spoke to each other — ending their friendship that started when they were 15 and 16, Morgan told the jury.

“I draw my line at physical abuse,” she said.

“I don’t know why (Ventura) doesn’t reach out to me. I’m sure she doesn’t have the same phone number anymore.”

Ventura’s relationship with Combs ended in 2018 and she has since sued him over his abuse, garnering a $20 million settlement.

Last week, she spent four days on the stand as the prosecution’s star witness, unflinchingly detailing years of abuse by Combs and humiliating experiences in his depraved “freak-off” sex parties.

Morgan’s testimony Monday fleshed out the allegedly abusive relationship Combs and Ventura shared for more than a decade — as well as the aftermath of his notorious March 5, 2016 attack at the InterContinental Hotel in Century City.

The following day, Morgan said she was at Ventura’s Los Angeles home when her then-friend arrived with a black eye following the beating by Combs — who showed up 30 minutes later in a blood-curdling scene.

“He was hitting the door with a hammer to try to open it,” Morgan recalled.

Morgan said she was “terrified” when she saw Combs through the peephole — using the tool to try to break in.

But Ventura looked “numb,” Morgan testified.

“I was freaking out. I don’t think [Ventura] cared if [Combs] came in and killed her,” Morgan said.

The harrowing testimony by Morgan, who now lives in Los Angeles, also detailed two instances when she saw Combs’ alleged abuse of her now-former friend Ventura with her own eyes.

The first time, Morgan said she witnessed Combs “push” Ventura and thought she also saw him hit her while they were in the primary bedroom of the “It’s All About the Benjamins” singer’s Los Angeles home and she was standing in the entryway.

Morgan said she then left the pad with Ventura and the pair hid out on the front steps of a neighbor’s house for 30 minutes.

The second alleged assault happened around January 2013, when a group of friends including Combs, Ventura and Morgan were on a trip in Jamaica.

The fallen music mogul got incensed when Ventura took too long in the bathroom, Morgan said.

“Two minutes later, I heard screaming,” Morgan recalled, adding it was “terrifying.”

Combs dragged Ventura about 10 feet along the floor before Morgan grabbed her purse in case she had to run, she testified.

When she came back, Combs was outside with Ventura.

“I saw him push her on the ground and she hit her head on a brick,” Morgan recounted. “She didn’t move.”

Morgan said Ventura was lying in a “loose fetal position” and her eyes were closed.

“I thought she was knocked out,” she testified, noting Ventura appeared to be out for 20 or 30 seconds.

The two women bolted and crouched in a ditch for what felt like hours, as they hid from Combs, Morgan testified.

Morgan’s testimony dovetailed with Ventura’s assertion that Combs was a jealous, possessive partner.

She said Combs was jealous of Ventura chatting with “Black Panther” actor Michael B. Jordan.

“They were not together and [Combs] was jealous about it,” Morgan said. “I think [Ventura] was trying to leave [Combs].”

Combs faces up to life in prison if convicted on charges of sex-trafficking, racketeering and other crimes.

He has pleaded not guilty.