The folks at USGS would love to have a report on this non-native.  There are reports of Bannerfish off West Palm Beach, but no photos to ID which species of bannerfish.  Your fish is either Heniochus diphreutes or H. acuminatus.  Go to this web site to see a comparison:  http://www.reefcentral.com/forums/showthread.php?t=1626751.

The web site to report non-indigenous species is http://nas.er.usgs.gov/sightingreport.aspx.

Carol

Thanks!  I had reported it to Reef, but just sent a report to USGS too.