The best part is that you can get the car for free as long as you have played either game on Xbox One by August 1st, or played Forza Horizon 3 on PC.
If you are getting the car for playing Forza you will receive a message in-game. If you are receiving the car because you played Final Fantasy then you will get a download code through Xbox Live.
They have yet to announce if there will be any other ways to receive the car. In the past, those that have missed out on free content have gotten another chance to receive it through in-game events.
Forza Horizon 3 is already a great game on its own, but it is great that they keep supporting the game with some really good DLC. So, if it’s been awhile since you’ve played now would be a good time to jump back in, and check out some of the content that has come out since.