Back at the turn of the millennium, they were just a bunch of kids — some with a bit of professional acting experience, most completely raw — that were fortunate and talented enough to be cast in "Harry Potter and the Sorcerer's Stone." The film conjured up almost $1 billion at the worldwide box office, and as "Potter" movie after "Potter" movie went into production over the years, Daniel Radcliffe, Emma Watson and the rest of the core cast essentially grew up together.

Almost a decade after their first witch-and-wizard adventure, the child actors have morphed into young adults — and the story lines have matured along with them. "Harry Potter and the Half-Blood Prince" (in theaters July 15), the sixth film in the franchise, presents all manner of love triangles, broken hearts and blossoming relationships. The difficult trick for the cast, though, was jumping lips-first into these romantic scenes with co-stars who had become like family.

"The snogging snuff is always a bit challenging, because they've grown up together, so when you get Bonnie [Wright, who plays Ginny Weasley] and Dan having that first snog together, it's a bit like brother and sister," director David Yates told MTV News at the movie's New York premiere on Thursday. "You've got to just encourage them to think about their characters."

"I've known her since she was 9 and I was 11," the 19-year-old Radcliffe said, adding that Wright looked gorgeous making her way down the red carpet. "So, that was kind of weird at first. But we got used to it. We got over it pretty quickly."

Wright herself saw both the good and the ugly in making out with her childhood friend. "It helps, because you've known each other and it's not just a stranger," she said. "But then it's really weird when you're having to look at someone in a different way in a scene when they're that close."

The actors won't escape the task of playing kissy-face on set just yet. The final two films — the two parts of "Deathly Hallows" — will keep the romantic elements front and center.

"I did the kiss with Emma a couple weeks ago, and it was quite strange," said Rupert Grint, who plays Ron Weasley. "I've known Emma since she was 9 years old, and it felt a little bit wrong being that way with her. But it was over quite quickly."

While Watson also called the kiss scene "really awkward," she did compliment her partner. "He's a gentleman, and he was a great kisser," she told us.

For Yates, who's worked on the series for years, watching the actors grow up together has been one of the most captivating aspects of the entire experience. "You're seeing them develop and evolve," the director said. "In their own lives, outside the film set, they're obviously having their own experience of love and love life. I encourage them to bring that into Hogwarts and share it, to help their acting have a basis in reality."

Check out everything we've got on "Harry Potter and the Half-Blood Prince."

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