NATALIE FULLER

When Natalie and Simon Fuller were married in Napa, California, in 2008, they did so under an 80-year-old olive tree that was a gift from Stephania Kallos and Abigail Turin of KallosTurin, the architects who designed their new home in Los Angeles. "They bought us the tree as a wedding present and craned it up to Napa," explains Natalie, who wore a custom-made "old Hollywood" Roland Mouret gown. "It was built into the deck where we got married. Then they brought it back and we planted it in our yard. So," she laughs, "the tree was at our wedding."

That olive tree is almost as well traveled as Natalie. She and Simon spend six months a year on the road—Simon overseeing his entertainment kingdom, encompassing American Idol, So You Think You Can Dance, Web site Fashionair, and the labels RM by Roland Mouret and Victoria Beckham (he's known Beckham since he signed the Spice Girls in 1995), and Natalie, 34, consulting on interiors projects and designing and overseeing the couple's six houses in London; Sussex, England; Nashville; Punta del Este in Uruguay; the South of France; and, the newest addition, a rebuilt 1920s home in Beverly Hills.

Unusually, it's traveling that the chic blonde (and streamlined packer) Natalie credits for keeping them close. "We spend about four months in the States, a month in France in August, and a month in January somewhere for the holidays," she explains. "It's amazing to always be happy where you are and excited about it." Simon adds, "One of the secrets to our marriage is we are very rarely apart. We are lucky enough to have houses all over the world, so when we travel, we can still have a home life. It never feels like I am traveling for work."

Natalie's closet has benefited from her international mobility. She attends the Paris shows, is indulging a new obsession with designer Andrew Gn ("I never feel overdressed in his pieces"), and adores Lanvin. "I wore a beautiful long emerald-green silk dress to the British Fashion Awards. It was comfortable but chic." In Los Angeles, she visits cult vintage retailer Rita Watnick at Lily et Cie. "I've committed to buying one or two major, iconic dresses from her a year, like '50s and '60s Dior. I just bought a black Jean Dessès dress. It's just an incredible piece of history and artistry." When in Los Angeles, Natalie indulges her "hippie tendencies" and dresses down during the day, but at night "all bets are off," she says, "and you can bust out any outfit you want."

These days, the Fullers are spending more and more time in L.A., home of the American Idol empire. The house, transformed into a heady mix of crisp modernism and vintage opulence, has also hosted an Idol or two around the grand piano, which was once a gift from Simon to his late mother for her 80th birthday. "The piano actually gets played in L.A.," Natalie says. "We had a party not long ago where we had the top 10 Idols from last year, and they all got on the piano and had a jam session."

The manse, complete with a Beverly Hills Hotel-style deck and bar, is built for entertaining, and Simon handles the music while Natalie handles the margaritas. On Simon's playlist right now: "Stevie Wonder's Innervisions, Marvin Gaye, the new Alicia Keys album, Beyoncé, Muse, Lady Gaga, and David Bowie's greatest hits." What about the Spice Girls? "Oh, I save them for New Year's Eve."

The couple moved into the house directly after their honeymoon. "I remember coming back and standing in the front yard with chandeliers everywhere. They were in a hundred pieces," Natalie says. But soon enough, the original 1970s Venini flower chandelier was installed in the wine cellar, while fixtures from the 1940s were installed in the formal spaces.

The wine cellar is perhaps Natalie's favorite room. "When we were married in Napa, instead of asking people for gifts, we did a wine registry. All of the wines in our cellar are presents from our wedding. So whenever anyone comes over, I have a list of the wines and we can open the bottle that they gave us for the wedding." Wine and song, check. "Yes, we're winos, foodos, travelos," she says with a laugh. "That room is very personal to me."

Her other favorite rooms are the bedroom ("With the chandelier and the soft color palette, it's just a really lovely room to be in") and the formal living room. ("It captures a bit of glamour but makes it warm.") Standouts are an exquisite three-piece gold-plated Hubert Le Gall mirror from Themes & Variations in London and the two 1950s first-class railway seats designed by Gio Ponti and Giulio Minoletti for what must have been one of the chicest commutes: Milan to Rome. "When I had them reupholstered, they still had the flue in the arm where the ashtray would lead," Natalie says. But take no liberties, visitors: "We do not allow smoking on the train chairs." In case anyone doubts the chairs' provenance, Natalie grabs her Gio Ponti coffee-table book for proof.

The adventure of finding such unique pieces was the joy of putting the house together. Natalie is not a fan of the instahome. "We hunted down dealers in London, went to the market in Paris, and found each piece over a span of time. Every piece has a story and a great memory attached to it. To me, it doesn't feel like a formal house. It just feels like a place where you want to hang out, a beautiful, sexy environment. It feels authentic."

The Fullers maintain they are always in agreement about the decor. Except for the time they went to India "and I wanted to buy all this amazing antique furniture I found in Jodhpur," Simon remembers. "Natalie said, 'Go easy, we have nowhere to put it,' but I of course went and bought two containers full and had them shipped back to England." He adds ruefully, "To this day, they sit in storage, although one day I will find a room that requires 10 incredible antique doors and has seven walls to hang all the art and enough space for eight tables and a dozen chairs."

"Simon's got incredible taste," Natalie adds. "He went to art school, so he's really good at thinking graphically and conceptually." But other skills come in handy too. She says, "I'm such a Virgo that at this point, he really trusts me, and it's something that I really love doing."

Natalie has also opened Simon's mind to fashion. Given he was the mastermind behind the Spice Girls, he has had a relationship with Victoria Beckham for years, but it was Natalie who introduced Simon to Roland Mouret. She first met the designer when she passed by his studio in London one day and just rang the doorbell. "I had heard about his Galaxy dress, so I said, 'If you're ever having a sample sale, I'd love to come.'" Skip to Natalie coming home—with many bags—from said sale. "I said, 'Simon, this is a Galaxy dress. Very important!' Things just evolved in that way."

Also evolving is the Fullers' new apartment in New York's Plaza hotel, which will be ready by the summer. "It's looking incredible," Natalie says. "It's got the most stunning views. You're a floor or two above the tree line, so Central Park is your backyard. "

Whether she's in L.A., New York, or London, Natalie does allow herself a wide-eyed Eloise moment or two. "It's really such a privilege, and that's why we want to share things with people and have it be accessible and fun. I want everybody to come into our home and feel like it's theirs as well as mine and Simon's."

For anyone sitting on the deck of the Los Angeles house, under the olive tree, margarita in hand, that emotion should not be hard to encourage.