In "Harry Potter and the Half-Blood Prince," Daniel Radcliffe and his co-stars went rom-com, embracing lovey-dovey storylines about broken hearts, unrequited affection and what it feels like to finally connect with your true love. It worked: The film raked in over $300 million at the domestic box office, making it the second-biggest film of the year so far and the highest-grossing "Potter" flick since 2001's "Sorcerer's Stone."

With the DVD hitting shelves this Tuesday, Radcliffe and the rest of the cast spoke with MTV News about why they believe "Half-Blood Prince" made so much freaking money ($929 million worldwide). Their answer was clear: romance!

"I do think people responded to the fact that there was kissing and hormones and all that kind of stuff," Radcliffe said, singling out Rupert Grint's turn as Ron Weasley, the mop-haired wizard who finds himself the object of the affections of both Hermione Granger and Lavender Brown.

"It's a very lonely film and kind of a hard film for Harry, whereas Ron's just happy because he's getting his rocks off with Lavender now," Radcliffe laughed.

So, how did Grint deal with all that onscreen snogging? Uncomfortably, it seems. "The kissing scenes are always quite embarrassing, but we got through," the actor admitted. "You always feel a bit self-conscious, because there's a room full of people and it feels quite mechanical."

Awkwardness aside, Radcliffe maintained that without the rom-com plotlines, "Half-Blood Prince" would have been a rather dull affair. "If you take out the romantic storyline, it's pretty much two and a half hours of me looking lonely," he said. "That's all that's left."

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

For breaking news, celebrity columns, humor and more — updated around the clock — visit MTVMoviesBlog.com.