Lady Gaga Celebrates Manager Bobby Campbell's Wedding With Fiancé

Lady Gaga was in celebration mode this weekend ... 'cause TMZ has learned she and her fiancé, Michael Polansky, stepped out for date night at the wedding of her longtime manager and close friend, Bobby Campbell, and his husband.

Sources with direct knowledge tell TMZ ... Gaga and Polansky attended the Saturday night ceremony at the Walt Disney Concert Hall in downtown Los Angeles, where Campbell and Robert García tied the knot surrounded by family and friends.

We're told Gaga kept a low profile throughout the evening, blending in with the rest of the guests instead of stealing the spotlight. And despite her superstar status, our sources say she did not perform during the reception.

Instead, we're told "Gypsy Woman" singer Crystal Waters provided the night's entertainment, getting guests on their feet during the celebration.

Campbell and Gaga go way back. He's managed the pop icon for years and has helped steer some of the biggest moments of her career, from chart-topping albums and global tours to her Oscar-winning era and recent projects.