Weird Al Yankovic -- Prince Has NO Sense of Humor

It's the question Weird Al Yankovic fans have been asking for years -- Why won't Prince let him spoof any of his songs??

Well, now Weird Al is finally shedding some light on the topic ... saying the guy has no sense of humor.

Al was at LAX, where he explained that he ALWAYS asks for permission from the original artists before he spoofs a song ... but Prince has never given him the green light.

Yankovic said he isn't bothered by the rejection though -- saying, "There's plenty of enough people that HAVE a sense of humor."