B190 FLC HAVE NMAC WITH SINGLE ENG CESSNA AT DEKAL INTXN; WHICH IS IN THE CONTIGUOUS UNITED STATES ADIZ.

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ENRTE FROM ELH TO FLL; WE WERE GIVEN A DSCNT FROM 14000 TO 4000 FT. BEFORE REACHING 4000 FT; ZMA ADVISED US WE WERE TO EXPECT HOLDING AT 5000 FT; AT DEKAL INTXN; 20 MI ON THE ZBV 300 DEG RADIAL. WE LEVELED AT 5000 FT AT DEKAL INTXN. OVERHEAD THE ZBV VOR; THE TCASII SHOWED AN ACFT AT THE SAME ALT APCHING US. WHEN THE ACFT WAS WITHIN 1 MI; I ADVISED THE FO; WHO WAS AT THE CTLS; TO TURN AWAY TO THE L AND DSND WHILE I CALLED ZMA ASKING 'WHO WAS FLYING IN THE AREA?' WHILE IN THE PROCESS OF MAKING THE RADIO CALL; I SPOTTED THE TFC TO THE R OF US; AND ADVISED THE CTLR THAT I HAD THE TFC IN SIGHT. IT APPEARED TO BE A CESSNA SE. THE TCASII HAD SHOWN THE ACFT CLBING THROUGH 5000 FT. THERE WERE MULTIPLE ACFT HOLDING ABOVE AND BELOW; DUE TO POOR WX AND NO ARRS INTO MIAMI OR FLL. THE TA IS WHAT ALERTED MY DECISION TO MANEUVER THE ACFT TO AVOID A 'LOSS OF SEPARATION' AND WHAT WOULD HAVE BEEN A MIDAIR. WE WERE WITHIN 200 FT AND NO MORE THAN 30 DEGS OF COURSE DEV; TO AVOID THE CONFLICT. I CALLED ATC AFTERWARDS; DUE TO THEIR REQUEST.