Of course there is a rule, that’s why everyone is trying to tell you what it is. In the section of the rulebook that is titled “Liberating a Territory” it states the rule clearly;
If the original controller’s (the power whose territory you just liberated) capital is in enemy hands at the end of the turn in which you would otherwise have liberated the territory, you capture the territory instead.
If you read the beginning of the Combat Movement section you will find that you have to end your movement in a hostile zone. In other words, you can’t attack your allies, friendly neutrals, or yourself for that matter. Any movement into FIC by ANZAC would be a non-combat move in which you wouldn’t conquer it, or a combat move into it under axis control where you would either liberate it for France if they still had a capital, or conquer it for ANZAC if France didn’t have a capital.