I did a little surfing, and as far as I can tell, here's the scoop..
Since his father is "head of state", i.e., King of Spain, as a "family member", he has Diplomatic status, and the same Diplomatic Immunity as his daddy...
Unless the U.S. State Department declares him "persona non grata"..
I doubt very much whether the US State Dept. is gonna do that..
The Crown Prince seems to have not only a very good reputation, but apparently is just as important in europe as Prince Charles of England..
I have no doubt he has diplomatic credentials of his own, completely independent of his father's..
He's got a sister (princess-type) that often lives in the U.S. as well.. good looking woman..
MMmmm, yes, the Infanta Cristina, she's yummy...
The Infanta Elena, on the other hand... well let's just say you can tell that she and Prince Charles are related.
-ccm