Should I tell my mother? What does Islam say about this?

I feel so embarrassed sharing this, but recently I stumbled upon something on my father’s phone that I wish I had never seen. He’s been involved in a relationship outside of marriage, in the city where he works. My mother is the most wonderful woman, and now I’m torn. What should I do? Should I inform my mother, or stay silent to avoid tearing the family apart? I’m seeking guidance from an Islamic perspective-what is the right course of action here?