By TIM NIXON. Bum-believable ... Justin Bieber
Gregg DeGuire/FilmMagic The rear side of the teen titan's underpants were entirely exposed as he crouched down to greet fans onstage in California.
Crowds at The Home Depot Center – where LA Galaxy play their football – aren't used to seeing pants displays on the pitch.
But Justin's army of besotted followers lapped up the sight of their pop idol's derriere.
The Boyfriend star was performing at 102.7 KIIS FM's Wango Tango at the Carson arena, where he walked out to an ear-piercing chorus of screams.
Meanwhile, Justin – who's dating Disney beauty Selena Gomez – has a released a special song for his mum Patti today.
Meet and greet and cheek ... Justin Bieber
Gregg DeGuire/FilmMagic The singer revealed he'd penned his tribute last month but waited to release it on Mother's Day, which falls on May 13 in the US.
He said: "I wrote a song for my mum. She had me at the age I am now.
"It's about the struggles she went through and how brave she was, and I think the world needed to know that."
Bless his little cotton pants...
The rear deal ... Justin Bieber
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