then the free action simply takes place after the turn ends.
Taking away the free attack the PC rightfully earned is totally unpracticable and unfun. Any DM here who actually does that? I prefer common sense.
The free action can't take place after your turn ends. What allowed you to use the free action? That trigger that occured on your turn and your turn is over now. Might as well take your free action next turn, after all it triggered before and it just wasn't used.
We don't allow it in our games. We prefer common sense when it doesn't go against the rules. The rules are that when you charge you're done taking actions on your turn. Certainly everyone can see that.