ex-husband in-law
The ex-husband of your current wife and the father of your step-child. He usually acts like he is one of your best friends since you are now sleeping with the woman he didn't want and raising the kids he didn't seem to have time for when he was married to her. The ex-husband -in-law nomenclature does not apply to the man left behind from a failed marriage caused by an adulturous woman.
My ex-husband in-law came over to pick up my step-daughter and I just about couldn't get him to leave the house. He kept wanting to talk about the game, or the race, or tell me about his new girlfriend. I swear, he tries to act like I'm one of his best friends.