Is it normal that i'm now super attracted to my sister?

Well I guess to start off my sister and I are year apart so we never really has that bathe or shower together phase of childhood. We are 4 years apart sometimes 3 depending on the time of year. My sister has always been one of the popular or liked girls at school. There were rarely kids talking poorly about her. She is pretty always had guys crawling over her. That's what my dad said it was like for my mom in high school too. But I just got home from college and I accident walked in on my sister changing... and I saw something that was not only shocking but appetising. My sister is a transsexual. I would have never of guessed it because she is so feminine. Her face, body, everything not what you would expect for a shemale. She was super embarrassed and seemed upset that I had finally come to realize she had a penis, pretty nice one too. I tried to comfort her by telling her some guys like it and she'll still live the life like most women do and what not. But then she asked my opinion about it and I was kind of hesitant to tell her so I avoided the question. But I find Shemales attractive, I'm just one of those guys. I've experiment with a few but nothing super serious. But now my younger attractive sister is one? I got super turned on by this. We've started hanging out more. Becoming closer and what not and now I'm just waiting here sometimes pleasuring myself thinking about my sister and me having sex. Now I believe this would never have happened if she didn't turn out to be a transsexual but this news just pushed me to the line of what might happen. Is it normal that this turns me on? Should I act upon my sexual desires?