"I'm feeling a bit guilty, to be honest, as I've made them wait in the rain," the star, 19, said about the fans, some of whom had camped overnight for a glimpse of him and costars Emma Watson and Rupert Grint, who recovered from a bout of swine flu to attend.
And while usually mum on his dating activities, Radcliffe did let slip, "I've been out with a couple of women who have been older than me. I think it's the maturity thing more than anything else, but that was when I was younger – girls my age are now mature, so it's great. I've widened the field!"
Jessie Cave, who plays Lavender Brown in this sixth installment of the Potter franchise, told reporters on the red carpet that Radcliffe has a unique trick up his sleeve when it comes to romance.
"Daniel loves poetry, it's definitely a passion of his," she said, "and I think he would suit that sort of poet lifestyle, he's very dramatic and witty and very, very clever."
Watson U.S.-BoundWatson, 19, who'll be studying in the U.S. this fall, said, "I'm really excited, I can't wait." In terms of seeking advice from a young American celebrity graduate, the teen said, "I would love to talk to Natalie Portman, she's a big idol of mine."
Sporting long, flowing Ossie Clark vintage 1970s dress with a plunging neckline and Chanel jewels, the teen actress described her recent stint as a Burberry model as "so much fun."
Some of the stars wore white ribbons in honor of murdered costar Rob Knox, while just about everyone – including Maggie Smith, Alan Rickman, Gary Oldman, Helen McCrory, Jim Broadbent, Michael Gambon and Robbie Coltrane – took refuge inside the cinema once the skies again threatened to open up.
With reviews that read like Valentines from the British movie critics, Half-Blood Prince opens in the U.S. on July 15, and there are two more installments still to come.