may be a young man, but at 20 he still succumbs to giggling fits. The happy prince cracked up at a photo shoot with dad Charles and big brother William in July that was originally set up for the royal Christmas card. (The Palace released one snap early in honor of Harry's Sept. 15 birthday.) "They were not laughing at anything in particular. It is just the way they relate to each other," said photographer Mario Testino. Not that Harry doesn't have a grown-up side. He spent his summer playing polo, partying and locking lips with old flames but also made an emotional documentary about his work with AIDS orphans last winter in Lesotho, which airs in the U.K. Sept. 19. "When he is old and gray," says his Lesotho host Prince Seeiso, "he can look back and say he had an impact."