Justin Bieber at “Christmas in Washington” taping Sunday at the National Building Museum. (John Nowak/TNT)

The downside of fame includes pesky paternity suits. The upside? Justin Bieber walked away from a shopping trip at American Apparel with a bag full of free clothes.

The 17-year-old pop star, in town for Sunday’s “Christmas in Washington” taping at the National Building Museum, stopped by the Georgetown store Saturday afternoon with a few burly bodyguards in tow; girlfriend Selena Gomez stayed in the waiting car.

Bieber — a fan of the casual, logo-free clothing — browsed around the store and picked up hoodies and other pieces. But no wait at the register for him, we’re told: Store employees comped the whole haul. Biebs didn’t pay a dime. A company spokesman confirmed that he left with a selection of T-shirts, hoodies, thermals, underwear, beanies and a Henley.

So, how does that work, exactly? We’re told that staff called their boss as soon as Bieber walked in, and company CEO Dov Charney authorized the giveaway because Bieber is a loyal customer of the brand.

Or . . . because he’s an international superstar? Fans went nuts when they spotted Bieber on the streets of Georgetown, tweeting their sightings and congregating at the scene.

Bieber’s manager, Scooter Braun, told us that the singer has a “great relationship” with American Apparel because Bieber is often seen wearing the store’s hoodies. It’s unclear how often he pays; Braun said Bieber’s staff never asks for free items. But hey, Bieber gets new stuff, and the brand gets free publicity.

But the real money shot for paparazzi following the teen couple around Washington came when they caught Bieber giving Gomez an affectionate squeeze on her rear.

Read more: Justin Bieber paternity saga: Your questions answered, 11/7/11

Justin Bieber, Jennifer Hudson, others take the stage at ‘Christmas in Washington’, 12/12/11