Once flying into YMMB in single from YNAR in CTA, we were vectored over Tulla' at 6000' then out over the bay descending to 4000'. A Cathay Pacific 747-400 was departing to the south. My rear seat RHS pax called it out to me that he was there. We watched as it climbed closer to our alt on a similar heading, only about 2-3nm away. At about 500' or less below us, ATC gave the CX747 an immediate right turn and me an immediate left, then asked me if I wanted to submit a report on the breakdown of separation. I replied that we had the 747 in sight the whole time and enjoyed the close up view of it in flight, to which the ATC guy seemed relieved.