Horny brother masturbates to watching his redhead sister being anal fucked

I have always had a thing for my older redhead sister. So when I heard her on the phone planning on meeting her boyfriend in a hotel I decide to follow her without her knowing. On getting to the hotel I waited till I started hearing moaning sounds before entering the hotel room. Once I entered the room my dick got hard from watching my sister being ass fucked. Few minutes into watching them I started masturbating.