Tabata has released a short story board that details the beginning of the game. The Kingdom of Lucis and Nibl--- sorry, Niflheim are due to sign an armistice to end conflict between the two nations. How will this armistice take place? With the wedding of Noctis and Luna, of course! But all is not what it seems. Once Noctis left Lucis to head to the ceremony, Niflheim pounced upon Lucis. SNEAKY.
http://www.dualshockers.com/2015/08/...ole-explained/
In the artwork we see Luna in what appears to be a wedding dress. I wonder if she is aware of her nations intention to strike Lucis while it was vulnerable, or if she thought that the marriage would actually get the go ahead and bring back peace?