First Time I Saw A Girl Naked

It was my friend's cousin. I was 13 at that time and she was 13 or 14. She was visiting my friend during the summer holidays. She'd just stay home with my friend's sister all day.

Few days into the holidays, I went over to my friend's house to return the game CD I'd borrowed from him. When I got there I saw his grandmother leaving the house. I told her that I wanted to return the CD. She told me that the whole family was out for the day. Since she knew me well, she let me inside and told me to close the door properly when I leave. Once inside I entered my friend's room and put the CD next to his PC and left his room. That's when I heard the bathroom door open.
And there she was. My friend's cousin. Standing there completely naked. Her body was still wet and she had a big towel wrapped around her head. Which was lucky for me as she couldn't see me standing there 10 feet away from her.
Within few seconds my mind went from realising what was I seeing to admiring the view to panicking. I knew I'd be dead if she saw me looking at her. I quickly stepped back inside my friend's room and hid behind the door. Through the small gap I could still see her. She stood there for fee more seconds then started walking towards the room next door which was my friend's sister's. She wrapped the towel around her body but not before I got a good view from behind. I'd seen her before in jeans, shorts and dresses but seeing what was underneath made my brain go numb.

I started to leave but something painful made me stop. I saw a very noticeable tent in my shorts. Grabbing my boner I left my friend's house as quietly as possible.