Sister in law

My sil lived with us for a few weeks. It was torture watching this little 18 yr old 100 lb red head walk around. One day I'm with the k**s downstairs and my wife calls down for dinner. The k**s went up as I finished watching something on tv. What happened next floored me. My sil comes downstairs from the shower with the shortest towel wrapped around her, when she opened the door she sees me and froze. I told her it's ok I won't look, I lied. Her little ass was totally exposed as she ran into her room. I had to follow ,especially since she left the door open a little bit. I went in and undid her towel leaving her naked in front of me. Her nipples were so puffy as I knelt down to kiss them . Just as I was sliding my fingers into her little red pussy my wife,her sister called out to come up for dinner. Nothing more happened. It was so good