The gist of the story was that Matt was making it with Miss Kitty, The Madam. They never really showed it though, it started as a family show.
I thought there was a made for TV movie that had him searching for a kidnapped illegitimate daughter. Or am I remembering wrong?
Just checked Wiki: Movie number two, Gunsmoke: The Last Apache (1990), had Learned reprising the role of "Mike Yardner" to divulge that Matt sired her daughter, who is now a young woman named Beth.