Who was that, one may ask?

A very good question. He was this preteen whom Brenda Morgenstern babysat for that his divorced father Joe picked up and took an interest in Brenda's visiting sis Rhoda! Yet, Donny didn't attend Rhoda & Joe's wedding ( and the only relative of Joe's who was there was his mother who attended solo despite Rhoda having met BOTH Joe's parents before the wedding and no friends of Joe were there either despite Ida packing her apartment with Rhoda's entire extended family and Minneapolis friends and Phyllis )- and he only appeared in one episode after his father's marriage to Rhoda (the episode in which Rhoda thought she might be pregnant and wasn't ready for that to happen). Then NOTHING. Not only does he have zero interaction with his new stepmom Rhoda but his dad isn't depicted spending any free time with his son and there's nothing to indicate that changed after he and Rhoda split! Oh, and Brenda never babysits him or anyone else again!

Ironically, the scriptwriters whined about how tough it was to write for the newlywed Rhoda (and saved most of the broader comic material for Ida and Brenda) but why were there no other attempts to have Rhoda interact with her new stepson (or,for that matter, Ida dealing with her stepgrandson)? I would think that that would have been worth some good episodes in the comedy but that wasn't to be.