According to TMZ, the 29-year-old Me & U singer had told the 46-year-old music mogul their relationship was over as they drove home.
But Diddy was reportedly not happy with being dumped, and is said to have grabbed her phone in a rage. According to reports the rapper then jumped out of the car in Beverly Hills with her phone, before Cassie sped off home.
Diddy is said to have returned home with her phone later, before taking two cars and leaving.
However meanwhile Cassie had told her mother about the incident who called the cops.
Police reportedly rushed to her home after Diddy had already left, but retreated once they heard she had got her phone back.