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For a couple with their hands full raising three kids ages 3 and under, the honeymoon's still not over for Heidi Klum and Seal. They whisper in each other's ears, entwine their arms, exchange flirtatious laughter—and that's just during a photo shoot not far from the home they share in Beverly Hills. "Often with relationships, you forget what you were before you had kids, when you were the most important thing in each other's life," says Seal. "With us, we never lose sight of romance and having fun."

Still, few couples elevate the art of romance quite as grandly as these two. From the 14,000-ft.-high Canadian glacier where Seal, 44, proposed to Klum, 34, in 2004, to the beach of Costa Careyes, Mexico, where they renew their 2005 wedding vows each year, the pair are hardly shy about expressing their passion. Klum, after all, recently made headlines after telling Oprah Winfrey about first laying eyes on her future husband's "whole package" in skintight bike shorts.

This month finds the supermodel-rock star duo juggling both the Nov. 14 fourth season premiere of Project Runway, Klum's Emmy-nominated Bravo series, and the debut one day earlier of Seal's new album, System, which is already being praised as a return to his early '90s dance-floor roots. Away from the studio and the runway, the couple are most comfortable in their roles as parents to their three children: sons Henry, 2, and Johan, nearly 1, and daughter Leni, 3. (Leni's father is Klum's ex-boyfriend, Italian businessman Flavio Briatore, but Seal is raising her as his own.) Between trips to the pumpkin patch and preparations for the holidays, it's a bustling, joyful time for the brood—which is exactly how Klum and Seal like it. "Deep down we both always wanted the same thing: to have a family with a lot of children," says Klum. "We knew we could do that together." The pair took a break from work and child-rearing to share their five secrets to finding—and fanning—a red-hot marriage.

SECRET NO. 1
FIND COMMON GROUND

"We come from completely different upbringings," says Klum, who grew up in a western German town with a cosmetic executive father and hairdresser mother before being discovered in a modeling contest at 18. "I had a very normal kind of childhood where we would have breakfasts and dinners together and talk about our days. It was all very rosy. He comes from this whole other world."

Born Sealhenry Samuel in London to Nigerian immigrants who split up shortly after he was born, Seal was raised by a British foster family until age 4 (see box). Reclaimed by his mother, he was then shuttled between her and his father—whom he says had a violent temper—until he finally ran away at 15 to make his life on the streets of London. Yet "the polar opposites in our background almost make us so alike," says Seal. "She has certain values that come from the security of her family structure. I have the same values by not having had [that structure], just knowing that's what I needed." Discovering that their differences have ultimately proved unifying "just never ceases to amaze me," says Seal. Adds Klum: "It is nice to be proved right that you did want the same thing and picked the right person to get there with."

SECRET NO. 2
SEIZE THE MOMENT

After first spotting Klum at an awards show in England in 2003, "I remember thinking to myself, 'Wow, man! Who is that girl? Whoever the guy is that goes out with that girl is a really lucky guy,'" recalls Seal. A few weeks later they ran into one another in the lobby of Manhattan's Mercer Hotel—Seal was returning from a workout in his now-famous bike shorts—and Klum spontaneously invited him to join some friends for dinner. "I just think if you have an emotion and you let that go, that moment might pass," says Klum. "And if you don't open the door for the person to come in, it's just like, 'Nice to meet you. Goodbye!'" If she hadn't made the first move, "maybe none of this would have happened," she notes.

SECRET NO. 3
TWO WORDS: COMMITMENT AND RESPECT

After a few group dates, "we were sitting at dinner one night and our hands touched," recalls Klum. Says Seal: "That was it."

"It was the first time we touched," continues Klum. "We were, like, under the table and no one knew that we were holding hands. My heart was going 100 miles an hour."

"Mine too," says Seal. "It was right out of high school."

Admittedly there was a major complication: Klum would soon find out she was pregnant with Leni. But it was hardly an obstacle for this pair. "If you are ready [to commit], do you have the courage to go through with it and say, 'This is it'?" asks Seal. "We were committed to each other and we very much believed in each other. That is why we have what we have today."

Not that things are all romantic all the time. "It is ambitious to say that we wake up every morning and there are violins playing and angels singing," Seal says with a laugh. "She may annoy me one day; I may annoy her. But at the end of the day, there is a line I will not cross, and there is a line that she will not cross. That line is formed out of a mutual, fundamental respect. I think that is something you have from day one or you don't."

SECRET NO. 4
EMBRACE BOTH THE BIG AND THE SMALL GESTURE

Yes, this is a couple who got engaged on a glacier and who carve out romantic time around the world together. But beyond that, "he does things like open the door for you," says Klum. "I don't have to be this hot model [all the time]. We can just be normal with each other."

"She has never had to pretend in front of me," her husband confirms. "Of course I sing a few songs on the guitar to serenade her as you do...."

"As you do," says Klum. "Other men do not. As you do."

"But I mean, as beautiful as that girl I saw [that first time] was, I could just be myself with her," says Seal. "You can call love many different things, but that is how you know it: when you are with somebody and you do not have to be somebody else."

To that end, the pair often serve as each other's best critics. Working on System, "Heidi was like, 'The good news is, I know what you're trying to do. The bad news is, you ain't found it yet,'" recalls Seal of his wife's input. Adds Klum: "At the end of the day I love him and I can't lie to him."

SECRET NO. 5
PUT EACH OTHER FIRST ... EVEN BEFORE THE KIDS

When it comes to priorities, "I have a very, very simple approach," says Seal. "Heidi is No. 1 at all times, then it's the kids—as strange as that may sound—then it's health and career. I think that is the area where people get a little bit confused once kids come in and then the career takes over. But when we met, it was just her and I. Yes, there was a little one budding in her stomach, but it was just us two."

"And when the children are old and have their boyfriends and girlfriends—" interjects Klum.

"It will still be her and I."

"Yes, it will be you and I. And," his wife adds with a playful smile, "you will still be bald!"

See video from Heidi and Seal's photo shoot! Go to PEOPLE.COM/HEIDISEAL

  • Contributors:
  • With Karla Adam/London.