The 22-year-old actor and Billy, 47, were joined at the event by their other co-stars Michael Angarano and Nicholas Braun, as well as director Kyle Patrick Alvarez.
"They were both single and it just worked." PHOTOS: Costar couples Angarano's last serious relationship was with Stewart, 22.
The two began dating after they met on the set of during the 2013 Sundance Film Festival on Jan. The couple held hands and cuddled close for photographers.
Vincent before taking her relationship with her current girlfriend public."I've been deeply in love with everyone I've dated. " Stewart told that she is "so gay."Stewart told E!
News in March that her coming out "wasn't like, 'Let's do this thing that's going to be so important.' I just thought it was like a nice, light...