irony of fate is a very popular expression used to indicate an unexpected event and that serves to show that people do not always control what will happen in their lives and in the lives of other people.
Sometimes an irony of fate can happen when an individual does something wrong to someone else, or to himself, and then something very good happens to the person.
Irony of fate can be exemplified in several ways, for example, a bartender who is run over by drunk kids who have just left the club where he was working. It doesn't exactly mean the bartender was doing something wrong, but it was an irony of fate to have had an accident, precisely for those whose drunkenness he was indirectly responsible for.
Another example of the irony of fate is a couple who are dating and one of the parties always asks the other to lose weight but the latter never makes an effort. After an eventual breakup, this same person decides to lose weight all of a sudden and appears much more attractive than at the time of the relationship.