Illicit relationships

I have caught my father researching escort agency's twice and I am not sure how to handle it. The first time I did tell my mother and he denied going to any, yesterday my mother and I were gone visiting and on our return the front door was locked. When questioned he said he was sleeping. Later the Internet history revealed he was on those sights. Moulana please advise how do I deal with the situation without embarrassing my father or hurting my mother? I was in denial before and though he was only viewing pictures however I don't think that is the situation. Also my father is pious and I am so shocked.