Disclaimer: I haven't watched the video.
This is like the argument of how many angels can dance on the head of a pin. There is no one, right answer.
Some people will want to know. Some people already know, and want to feign ignorance (for many reasons.) Some people will claim you are lying, or will reconcile and blame you for any problems the relationship had. Many people fall into multiple categories.
Perhaps the best thing to do is to discuss it hypothetically in a group. "Hey, I saw this letter in Dear Prudence. If you were the wife, what would you want your friend to do?" In some circles, many people have that problem throughout the lifespan of the friendships. Even if she's not the letter writer, she'd have an inkling how her friends felt if it ever came up, and they'd know her feelings about it. If they are then upset, in denial, whatever, the bearer or suppressor of bad news can remind them that's what they once said they'd want.