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.