The “Beauty and the Beat” singer was in such a rush to get his party on for his 19th birthday (March 1) that he shed his shirt prior to arriving at his hotel.

“He was coming right off the stage – the show was done,” Justin’s manager, Scooter Braun, told Access Hollywood Live’s Billy Bush and guest co-host Holly Robinson Peete on Friday of the revealing photos circulating online. “He was coming off the stage and going to the hotel and he was literally running in because he wanted to get changed and go right out.”

The half-naked Biebs – sporting blue leather-type baggy pants and white briefs on full display – stopped briefly to greet a few of his fans before running into the hotel.

As for the Biebs’ saggy-pants swag, Scooter says his client’s days of drooping drawers are numbered.

“I think anyone over 25 can’t pull it off – actually over 20,” he said with a laugh. “He’s got one more year.”