Question about exposing affair to OM/OW's spouse

I see a lot of advice from people to people who have found out their spouse is having an affair, suggesting that they find out who the OM/OW's spouse is and confront him/her with their suspicions/findings. I was wondering if anyone here had this happen to them, where someone elses spouse came to you and told you about the affair that your wife/husband was having. Firstly, was it true. Secondly, how did you handle it, and what recommendations would you make for how to break the news so that it doesn't overwhelm the other person, or make them want to turn a blind eye and refuse to consider you could be telling the truth.

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