Stepdaughter Is A Nudist

I got off early a couple months ago and headed home for the day. My girlfriend was still at work, and I drove home.
I pulled into the driveway and parked my truck, got out and headed inside. Once I was inside, I went straight to take a shower, and when I had gotten out I was standing in the bathroom, drying off when I noticed something in the back yard.
I went to the window to see who it was, and when I parted the curtains, all I saw was a beautiful bare naked ass. My girlfriend's daughter was laying by the pool, fully nude!
I quickly averted my eyes and tried to ignore what I just saw, but the temptation was too much, and I looked again. She was laying on her stomach across one of the lounge chairs, which was just outside of the window.
He legs were slightly parted, just enough to see her shaven slit peeking out. My dick was so hard!