Queen Christina

Christina Aguilera's 22-month-old son, Max, is giving me a guided tour of their Beverly Hills home — which, on this late fall day, is plastered with Halloween decorations. "Green!" he shrieks delightedly as a grim reaper's head swivels round to reveal flashing emerald eyes.

Aguilera, whose extravagant rock-concert theatrics (three-ring circuses, 10-piece Roberto Cavalli costumes) outshine even Madonna's, is planning a party, complete with tarot card readers, punch-brewing witches, and an "insane asylum sexy dancer in a cage."

Still, it's hard to know where Halloween ends and real life begins. Aguilera and her husband, Jordan Bratman, bought the house in 2007 from Ozzy Osbourne, whose reality show unfolded in its head-spinningly gothic interior. All the doorknobs are embossed with crucifixes, the guest bathroom (reached via a gold wrought-iron gate) boasts a trompe l'oeil toilet disguised as a chair, and the centerpiece of the living room is a black lacquer, claw-foot pool table topped with shocking-pink felt. Into this setting steps the 28-year-old multi-Grammy-winning star: one of the most successful recording artists of the past decade, and one of the 20 richest women in the entertainment business.

If it weren't for her bleach-blonde hair, I wouldn't have recognized her. Because, besides being petite, she is, it seems, shy. She tells me that she has always been "intense and introverted" and that, as a result, she's felt like an outsider her entire life. Sia, the Australian singer who cowrote some of the songs on Aguilera's new album, Bionic (out this spring), reports in disbelief that Aguilera "is under the total misguided notion that she isn't cool; she's hyper-self-critical."

Go behind the scenes of Christina's photo shoot. Plus, check out photos from her 2008 shoot for MC when she was pregnant and naked on our cover!

It's 10 a.m. Aguilera doesn't think she's ever done an interview this early. Normally, she explains, "I would have had my lips on." But her signature crimson lips are nowhere in sight. She's wearing sweatpants and a flowy L'Agence T-shirt, and she walks with a dreamy sort of slouch. To escape the morning domestic bustle, we retreat to a pillow-strewn cabana, where John Coltrane is piped through hidden speakers. The previous day, Aguilera began rehearsals for her first film, Burlesque, a musical in which she stars with Cher — a woman she has idolized so much that a mutual friend told Cher that Aguilera wanted to "drink her bathwater." The acting experience was, she says, "kind of like my first day at school." She's been offered musical roles in the past but has been waiting, because "I didn't want to do something that was easy for me. I've actually had my character rewritten to be tougher and a little more spunky. But it's been quite the journey, let me tell you! Almost like training camp."

Not that Aguilera's been a slacker, exactly. Last year, she released Keeps Gettin' Better, a decade's collection of hits, and recorded Bionic. Now she has the movie to shoot and release, and a world tour. And did I mention she has an almost 2-year-old son? "It's really important that I'm the first thing he sees when he wakes up in the morning and the last thing he sees before bed," she says. Motherhood has inspired her to be lighter in her music. "I had a really hard time being light before," she explains. "I'd get a little weird about it being too cliché. My first record was very clichéd pop — what everyone else wanted." While her excellent second album, Stripped, was, she says, "inspired by a lot of pain," and her third, Back to Basics, "still had some sort of relation to my past," this new album "is just about the future...my son in my life, motivating me to want to play and have fun."

Aguilera has documented the torment of her own childhood in her lyrics: the "broken child" she was as a result of her now-estranged Ecuadoran-born father's abuse. Music, she says, was a large part of her "self-soothing." Growing up, Aguilera was such a big-voiced prodigy — the voice of Etta James trapped in the body of JonBenét Ramsey, with slightly less makeup — that kids mocked her mercilessly, threatened her mother, slashed the family's car tires. (Eventually, the family had to move.) Not only did she have incongruous technical gifts, but she also brought to the music she sang a kind of heartbreak well beyond her years. She may have first struck celebrity gold as a teeny-bopping Disney princess (who can forget the fortuitous Christina Aguilera/Britney Spears/Justin Timberlake triptych on the sixth season of The All-New Mickey Mouse Club?), but what's given her staying power is her professionalism, a great sound, and a willingness to make herself raw — an unusual combination, since the musically raw are rarely professional, and the hyperprofessional are rarely as gifted.

The range of people with whom she has collaborated is a testament to this: Alicia Keys, Missy Elliott, Lil' Kim, Diddy, Herbie Hancock, the Rolling Stones, the opera singer Andrea Bocelli. "Christina would have been important in music in any era," says Tricky Stewart, one of Bionic's producers and the man behind Beyoncé's "Single Ladies" and Rihanna's "Umbrella." "She's one of the most gifted singers on the planet." Sia tells me over the phone that she calls Aguilera a mad scientist, "because she's so technically brilliant, she scrambles my mind. She'll record a vocal track eight times, and she can hear a difference in every one. Anyone who thinks she doesn't have musical chops hasn't worked with her. The kid is a genius."

Read the rest of the interview in the February 2010 issue of Marie Claire, on newsstands now!