Anyone else's ex suddenly interested in parenting differently now that you're divorced?

When we were together, I was the one implementing bedtimes, screen time limits, homework supervision - basically everything. Now that we're split, she's suddenly the 'fun parent' with zero structure. My kids come back to me talking about staying up til 11pm on school nights and eating McDonald's for dinner. I don't want to be the bad guy but this inconsistency is wild. Do I just accept it or do we need to have a conversation about basic guidelines?