Are there cases where a guy is actually friends with his ex wife's new boyfriend/husband?

Before we got married, my wife and I had broken up for about a 5 month stretch. (We had dated 4 years through college before the breakup). She ended up "dating" a friend of a friend who I had always gotten along with. We went to the same gym and my friend was sharing a beach house with him that summer so I would crash there a bunch too. He was always so chill to me. It was odd but at the same time it was hard to be angry with him. Still friends with him now too, 10 years later.