Earlier this week (beg24Oct16) a photo of the glamour model passionately kissing actor/singer Pilot Jones leaked online, and the scandalous image appears to have sent Rob into a jealous rage.
The Keeping Up with the Kardashians star is now being probed by officials at the Los Angeles Police Department's Threat Management Unit for sending menacing text messages to his pregnant wife-to-be's alleged lover, according to TMZ.
Sources tell the outlet Jones fears for his safety after the 29-year-old sent him mean notes, including one that read: "Leave my wife alone. I'm not playing with you."
Apparently there are other texts, in which Rob threatens to physically harm Pilot if the actor doesn't stay away from Blac.
The contentious love triangle is further complicated as the exact date the smooch shot was taken is unknown - and could have been snapped earlier this year (16), when Blac and Rob temporarily broke up.
Blac and Pilot reportedly enjoyed a fling in January (16), and they have stayed in touch ever since. A representative for Jones previously insisted he and Chyna, real name Angela White, are just "very good friends".
Rob and Blac are expecting to welcome their first child together in days.
The pair made the pregnancy announcement in May (16) and on their reality television show, Rob and Chyna, the couple was filmed taking a paternity test, after which it was determined Kardashian was the father of their unborn child.