Whitney Houston's mother believes Bobby Brown's DUI arrest proves what she's been telling people all along ... he's just a bad dude.
Sources close to Cissy Houston tell us ... she's always felt Bobby was a cancer ... who infected Whitney's life with negative influences.
We're told Cissy felt "vindicated" when she found out Bobby was arrested for driving drunk on Monday afternoon ... and believes the incident is exactly why she wants Bobby to "keep his distance" from his daughter Bobbi Kristina.
The Houstons believe Bobbi K has been in a "vulnerable place" since Whitney passed ... and as one source puts it, "This is the last person she needs to be around."
Instead, we're told Cissy wants Bobbi Kristina to hang around "positive mentors" ... like Clive Davis.