Joe Jonas is going grocery shopping, walking along a busy commercial section of Hollywood. No one notices him, no tween girls shriek, as he weaves through the sidewalk traffic. Joe doesn't much look like a Jonas Brother anymore. Gone is his telltale luxurious sweep of black hair. Now it's cropped in a look one of his handlers likes to call "Top Gun-Tom Cruise," and he's wearing a rakish beard and mustache, along with skinny jeans that hang low enough to reveal the pattern on his boxers. These signs of testosterone seem to defy the boy band's squeaky-clean image—the three brothers wore "purity rings," pledging chastity until marriage. Joe, 21, looks all grown up. And there isn't a purity ring in sight.

"'Does anyone ever tell you you look like Joe Jonas?' I get that a lot," Joe says in his mild, soft-spoken way. "Or they'll say, 'You're so much cuter in person.' Or 'Where are your brothers?'" He laughs. "It's not like we wake up in the same bed."

Joe moved out of the home he shared with his parents and his brothers, Kevin, 23, and Nick, 18, a year and a half ago, to rent a house with some buddies in Los Feliz. But it was haunted, he says—"We'd hear footsteps"—and he often thought about getting his own place. Then, about nine months ago, he started dating Twilight star Ashley Greene, and the idea of a little privacy became more appealing. So last November, he found a bachelor pad in this part of town, which he likes because "it's like my mini New York. I got my gym a few blocks away"—where he's been working out five days a week with his trainer.

"I like to watch all the crazy characters in the neighborhood," he says. "I saw this gay homeless guy that got arrested. When the cops said, 'Spread 'em,' he was like, 'You'd like that, wouldn't you?'" Joe grins; he likes a good comeback.

In addition to hitting the gym regularly, Joe is also a fan of bars in the area, like the Bowery on Sunset, because it's "really laid-back." Wait a minute—didn't the Jonas Brothers, who provided the voices of cherubs in 2009's Night at the Museum: Battle of the Smithsonian, swear off alcoholic beverages?

Yes, but that was back when Joe was living with his mom, Denise, and his dad, Kevin Sr., a former evangelical preacher who now comanages the band. It was also before Joe decided to do a solo album, the first single from which will be released next month.

"I'm growing up, the fans are growing up," Joe says. "I've gone through a lot of stuff in my life so far. There are stories I haven't really been able to tell. When you're writing with three people, you wind up with a sound that might be—not average—but, you know, expected."

The moment he walks into Trader Joe's, the sound system starts playing "Year 3000," a Jonas Brothers hit from their first album, 2006's It's About Time. The boys' cheerful guitar riffs and boisterous voices fill the giant store. "I didn't call and arrange this," Joe says, amused, as he grabs a cart.

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Joe's apartment, a loft studio in a brand-new high-rise, is sizable, but it's modest for a young man who, with his brothers, made $35.5 million last year, putting them at No. 40 on the Forbes "Celebrity 100." There's a stunning 180-degree view of Los Angeles. There's a vintage Pac Man game, a Batman pinball machine, a Baldwin piano, and an 8-month-old English-bulldog puppy named Winston. There's a Warholesque painting of Mick Jagger by a local artist. Joe—who is known for his on-stage brio, his jumps and kicks and orgasmic facial contortions—has said that he idolizes the performance styles of Jagger and Freddie Mercury, "the big frontmen."

There's also a framed photograph of Joe and his brothers at the White House with President Obama and Paul McCartney—on the wall right by the front door, so you can't miss it. "I didn't know who to be more excited about," Joe says of the meeting, which took place last year when McCartney received the Gershwin Prize for Popular Song. The Jonas Brothers performed a cover of "Drive My Car" at the event.

"I heard [McCartney] told somebody, 'I want the new Beatles to come and play for me,'" Joe says, his chocolate-brown eyes growing wider.

Joe will tell you stories about famous rockers giving props to a band that the New York Times has called "among the most culturally important American rock bands of the last decade."

"Pat [Patrick Carney], the drummer for the Black Keys, I met him at a Kings of Leon concert in London"—coincidentally, it was at that same concert that Joe met Greene—"and he was like, 'I used to shit on you guys, but then I actually listened to your stuff, and you're so rad.'"

A Black Keys record is playing on Joe's turntable as he makes taco filling, simmering chicken in olive oil and lemonade. He's into cooking. After he got his own place, he says, "I fell in love with it. I became friends with a lot of chefs. I was a judge on Top Chef last year. It was a dream come true."

Then he pauses a moment; his thick, dark eyebrows knit together. He looks like a teenager again. "You know what? I forgot to get tortillas."

The taco filling winds up being wrapped into big pieces of lettuce—a fine, healthy, Asian-inspired solution. Joe stands at the counter as he tucks into his new culinary invention and starts talking excitedly about his solo album (which is as yet unnamed). He has been recording in L.A. for the past couple of months but says the idea came to him in the summer of 2009 when the JoBros were in Rome. "We were sitting in this beautiful Colosseum-looking hotel. And I was starting to think, 'I really wanna do a solo project.' My brother Nick did one. It wasn't really as big as..." Here he catches himself. Nick's solo album, Who I Am, released last year, received mixed reviews and sold fewer than 200,000 copies in the U.S.

"He wasn't really hoping for it to be huge," says Joe, who calls Nick "my best friend." "It was more for himself. He wanted to do a record that he really believed in. And so I was like, 'I would really like to make music that inspires me,' 'cause with the Jonas Brothers stuff, we can be constricted in what we can and cannot do.