@PUNKEY,
What difference does any of that make Punkey?
It seems as though all three of the people beyond the OP and myself who have posted are trying to make some connection(s) which don't exist or are totally irrelevant.
There aren't any dots to connect, but I suppose it's human nature to try to see a pattern or design so things "make sense"
In fact, it's the job of our neocortex to create patterns, to facilitate thought and communication. That's why we all have these seemingly random thoughts in response to events/stimulation we currently experience. Our brains are hard wired to travel through our brain maze, hitting dead ends, back tracking, finding a ghost of a connection, traveling that venue until it hooks up with a more concrete connection, until there is this weird connection between the apple over there and the orange over here exists.
It's why when we see a particular shade of a gray dress with a blue belt on a complete stranger we think of the friend of a neighbor of our Aunt Tilly's accountants hairdresser who used to live in Duluth, but moved to Sacramento, but didn't like it there because her daughter married a man who ate pistachio ice cream and left her for the grocery store clerk who would sell the ice cream to him every Saturday.
The fact he fathered a child is meaningless to his current marriage, regardless of the state of that marriage at this time, no matter how much we want there to be a connection so we can advise him to tell her, and cause all kinds of unnecessary, and perhaps harmful complications.
Is it because we're "supposed" to tell our spouse everything, regardless of when it happened in our lives, or if it has anything to do with any aspect of his current life? What, because of a mental burp that's got some connection a dozen, or 50 steps away from what is going on today?
For whatever reason, he had thoughts about this complete stranger he fathered 20 years ago, long before he had the life he had today, maybe because he saw a carton of eggs in the window of a department store display of kitchen tools.
Some things ya just gotta let go, acknowledging they aren't relevant to your life or relationships today.