The Princess and the Rocker

updated 12/05/2005 AT 01:00 AM EST

originally published 12/05/2005 AT 01:00 AM EST

With her burgeoning Olsen-twin-like empire of movies, clothing lines and multiplatinum albums and his globe-spanning tour schedule, Hilary Duff, 18, and her boyfriend of 16 months, Good Charlotte frontman Joel Madden, 26, have to savor their time together. PEOPLE'S Mark Dagostino caught up with the synergizing sweethearts (Madden co-wrote three songs on Duff's latest album, Most Wanted) over chocolate cake at Hollywood hot spot Geisha House to discuss their professional—and personal—collaborations.

What was it like working together on Most Wanted?

DUFF: You want to answer that?

MADDEN: It's fun. I'm really good at what I do. She's really good at what she does, so we do good things together.

DUFF: Don't be so modest!

MADDEN: She gets to record a different way and I get to make a different kind of music than I'm used to. I'm invested in it because of her. Me and my brother [Good Charlotte guitarist Benji Madden] worked on it. It's like hanging out with your friends.

Has Hilary influenced your work?

MADDEN: Not so much with music, but with other things that affect it. You know what I mean?

DUFF: That's a good answer [giggles]. They're amazing writers. I was so intimidated at first. He and Benj will be at my house and they'll sit with an acoustic guitar and in 10 minutes come up with a hit.

How are you two different?

MADDEN: The way we look, maybe. But besides the obvious?

DUFF: I'm really stubborn and he's kind of a pushover.

Wow. Joel, how do you feel about that?

MADDEN: I'm a sucker for her. No one can push me around—except for her. When she says something, it's like, "Whatever you want."

DUFF: We have totally different personalities.

MADDEN: She can go into a cheesy club and have a great time. She's like, "Let's make the best of any situation." And I'm like, "Let's just brood right here in front of everyone."

DUFF: I'm like, "Joel, smile. Joel, smile."

MADDEN: She'll take lemons and make lemonade. I'll just stare at the lemons and say, "What the...?" I'm not socially graceful sometimes.

DUFF: And I'm more athletic than him.

MADDEN: What?

DUFF: I'm more like, "Let's go on a bike ride! Let's go walking!"

MADDEN: She likes to do outdoor activities. I like to watch TV.

How do you stay in shape?

DUFF: I'm a Pilates addict. I never exercised before and when I did my American tour over the summer, my friend was with me and we said, "We're going to get skinny and work out."

Why?

DUFF: When I saw pictures of myself, I kept saying, "I don't like this, I don't like that." It's how girls are, you know?

MADDEN: I don't work out at all.

DUFF: Yeah, you do.

MADDEN: Like push-ups sometimes.

What was your best date ever?

DUFF: [To Joel] When you surprised me in Canada and we had dinner.

MADDEN: She was on tour and I showed up. It was across the country, not just an hour away. One time I flew to New York just to meet her at the airport so we could fly [back to L.A.] together for six hours, because we hadn't seen each other for two months.

People still bring up Hilary's feud with Lindsay Lohan. Does that infuriate you?

BOTH: No.

DUFF: It's silly.

MADDEN: They were both so young, and it's so nonrelevant now.

You both have clothing brands. How hands-on are you in the design?

DUFF: When I'm in New York, I do all the meetings and storyboards and draw things. I'll take them to my closet and say, "I love the way this was done" or "I like this color with this color."

What's the dumbest accessory trend in the last few years?

MADDEN: Small dogs. [Duff glares at him.] Just kidding. Just kidding!

DUFF: That did not make me happy. You'd better not mean that.

MADDEN: I like small dogs.

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