Long held secret that only my wife knows. Her daughter was 10 when we married. She started to develop when she was 12. My wife and I are well educated and borderline perverted and share some deviant interests. We were living in a townhouse at the time and did not discourage her daughter from parading around scantily dressed, so she was not inhibited but we were not blatant about our nudity together. If it seemed natural like getting dressed or after a shower that was okay.
The daughter was developing breasts and seemed happy to show them while being silly. I was not used to seeing young girls undressed and became quite interested. Once while I was taking a shower, the daughter came into the bathroom wearing only a white towel tied just above her breasts. For some reason I had left the shower curtain partially open and watched as she stood in front of the mirror preening. Her towel slipped down over her breasts and I remember feeling very stimulated. The bathroom door was open so I was not hiding anything from my wife.
On impulse the daughter decided to join me in the shower. I was now in a very awkward situation of making a scene or acting natural. Anyone with an imagination can understand my predicament. I acted as though this was not unusual but I believe she knew she was being bold and I knew I was getting aroused. With the water running I gave her the soap and we both lathered up. Her back was to me and I did not want her to see my growing erection.
Yes, I rubbed soap onto her back and she did not object when I continued with her shoulders and down over her breasts. I do not know if it was sexual to her, but it had become extremely sexual for me. I do not know how far I went with the soap but I did not intentionally try and stimulate her. She did not touch me. I diligently tried to hide my turgid penis but not entirely successfully. This was not mutual sexual play but the event has stuck with me as unbelievably erotic ever since. Of course I related the incident to my wife who actually thought it was pretty sexy.
For the next year or so as the daughter went through this phase, there were numerous occasions when there was full or partial nudity involving us and I must confess that I enjoyed horsing around with her as much as she enjoyed it. She enjoyed calling our bed the family bed and often before bedding down in her bed she would get in bed between us in a nightie or even naked. Nothing happened but I relive those times in my fantasies. She was truly an impish tease to me and I was able to manage my basest impulses that were relieved through masturbation and sex with my wife who I think found the entire situation sexy as it fueled her long held fantasy of incest.