I knew him and Kristen to be cordial. Very confuse as to what happened there.
I don't think it's hard to figure out. They were definitely friendly coparents. Lots of photos of them together, and Mark and Kristen's boyfriend together, and they even all traveled together. Right up until the time Mark started dating Anna. Based on how shitty she is to Kristen, her ex-husband and her ex's fiance online, I can't even imagine how much worse she is in private. If two divorced people coparent well until a new partner is in the picture, the new partner is more than likely the problem.