Diddy threatened to beat up Cassie's new boyfriend, personal trainer Alex Fine, MTO News has learned.

Two people close to Cassie claim that Diddy has sent "threats" to Alex - using mutual acquaintances to pass along the intimidation . The insider explained, "[Diddy] basically let Alex know, that when he sees [Alex] he wants a fade."

The insider added, "It's not a fade over Cassie leaving. It's just what [Alex] did was very disrespectful. Diddy hired him, and he [stole] his girl [Cassie]"

And Diddy made his point very obvious yesterday, when he posted this:

Last month Cassie announced on Instagram that she has a new boyfriend - her personal trainer Alex Fine. Before dating Alex, Cassie dated Diddy for the past 10 years.

According to folks close to Diddy, the music mogul believes that Cassie, 32, cheated on him with Fine. Cassie has been posting Instagram pics of her new bae to her followers -she even posted a photo of herself and Alex sharing a kiss on the lips.

But Fine and Ventura have known each other for months, the source says. The pair met when Diddy hired the bull rider to be Cassie's personal trainer before their split was announced in October, the insider claims.