I did the same thing and didn't have any problems what so ever with the regal I have. Actually, I didn't have any problems with any of my fish except after a week the yellow tang started to get frisky. What I did was put the Yellow in the hospital tank I have for about two weeks (same water conditions). Within that time I added more live rock and changed the tank around a little. Once the purple was comfortable I put the yellow back in and there weren't any problems. I'm a Tang lover but unfortunately tangs don't get along together very well unless you introduce them in a perfect order and make sure they all have PLENTY of swimming space and a good sleeping space.
If you have the opportunity, take the Regal out for awhile until the purple gets aquainted. Otherwise the tangs will get stressed and you'll have a major ICK outbreak.