'Mia' Feared Diddy Would Find Out If She Told Cassie About Her Alleged Rape

Diddy's former assistant "Mia" says she loves Cassie like a sister, but she didn't tell her about the mogul's alleged abuse because she says Diddy closely monitored their communications ... and he'd even put tracking devices on Cassie's car.

Mia took the stand for a third day of testimony Monday ... and, Diddy's defense attorney Brian Steel asked her why she wouldn't tell Cassie about Diddy allegedly raping her.

She responded by claiming Diddy could find out what she told Cassie ... saying he routinely took her and Cassie's phones -- presumably to search through them. He would even go so far as to put tracking devices on Cassie's car, with Mia telling the court ... "I’m not sure what he’s capable of. I was terrified.”

Mia testified against Diddy Thursday and Friday last week ... detailing Diddy's alleged treatment toward her while she worked as his assistant -- including the times she claims he sexually assaulted her.

Mia became emotional on the stand at times, breaking down in tears while testifying that Diddy forced her to perform oral sex on him during one incident.

While she admitted she talked about some of Diddy's alleged violent outbursts near the end of her employment with him, Mia says she never planned on discussing the sexual assaults publicly ... claiming she planned to take them to her grave.

Though Monday we learned she ended up telling prosecutors and federal investigators when they came to her about the Diddy case. Steel claims the conversation happened in June 2024, and Mia says she doesn't remember the exact date but "[she does] remember that horrible conversation."