The girl told the story of a couple from her hometown (she knows them personally). The banal story:

They have lived together for a long time and have a young son. After some time, the husband had a mistress on his side and from her he also had a son. Nothing predicted trouble until the wife learned about the mistress and arranged a scandal.

Do you know how I found out?

The faithful led their common son to introduce him to the "brother".