09/14/2011 AT 10:00 AM EDT
In the Big Apple, Justin Timberlake
had a guys' night out with Diddy
and a group of friends at the launch party for the fashion line Love by Isabel Adrian. And it was a late night: Timberlake arrived after 2 a.m., listened to music, drank champagne and danced to house music. "Justin was really letting go and enjoying himself," an onlooker tells us.