Identical Twins?

It was then that Jon's new twin sister entered the room. She was beautiful, Jon thought. She was dressed in a denim skirt and wore a tight top that showed off her cleavage. Jon thought he'd love this girl to be his girlfriend, if she weren't his sister. She smiled at Jon and Karen and spoke. "Karyn, Jessie? What are you two doing? We've gotta get to school now, or we're going to be late." She said. Jessie? Jon thought, who's Jessie? It was then he realized he was dressed in the exact same outfit as his sister...