The pop eccentric temporarily ditched her wild style, donning a pretty pink champagne halter-neck dress for Bo O'Connor's big day in Cabo San Lucas, Mexico.
Gaga, 27, clutched a bouquet of flowers and held the train of her friend's white bridal gown aloft as Bo exchanged vows with her man, reported Sun Online.
Despite conforming to the dress code, the singer still managed to turn heads with an eye-popping display of cleavage in her gaping design.
She mingled with guests at the plush resort and broke into a heartfelt smile as Bo and her boyfriend tied the knot.
The pair, who are starring together in 'The Other Woman', have been grabbing coffee breaks and dinner once filming is done.