Katy wore a cropped sheer blouse that showed off her bra underneath and a pair of matching blue shorts.
The pop star split from her husband Russell Brand in late 2011 and was later linked to French model Baptiste Giabiconi before hooking up with rocker Ackroyd.
The festival seems to bring out uninhibited celebrities. "Harry Potter" star Emma Watson attended the event a week ago with her new boyfriend, and Emma Roberts and "Glee" star Chord Overstreet also showed off their reignited romance at the event.
See more photos of Katy and her new boyfriend...