He's used to being the center of attention, but Justin Timberlake stepped aside Saturday night, letting girlfriend Jessica Biel enjoy her moment in the spotlight at a screening of her new movie, Hole in the Paper Sky. "Justin arrived in a separate car and met her inside," says an onlooker at the Palm Springs International Film Festival's Short Fest. "He was saying how excited he was to be back in Palm Springs to see Jessica’s film." Biel, who produced and starred in the film, arrived in a stunning one-shoulder Stella McCartney dress and was accompanied by the film's director, Bill Purple.Though Biel and Timberlake snuck out of the theater just before the film ended, the "couple sat together and watched the program of shorts." They were later seen at the Parker Palm Springs hotel celebrating with a group of friends. While fans gushed over the surprise appearance by Timberlake, Biel had her own wave of attention earlier in the night. "Before heading into the theater, several of the Marines from the [nearby] base were volunteering and asked Jessica to pose in a photo," says the onlooker.