Based off of this pic by Kaciart http://kaciart.tumblr.com/image/170695770838
What ever set up or justification you can think of, however it gets to that point, Ardyn is set for an arranged marriage with Prompto. Prompto isn't happy about it, and obviously neither is Noctis or the rest of the chocobros. Who are determined to make sure the wedding doesn't happen. And ultimately have to burst in during the ceremony itself to stop it.
Prompto/Ardyn, Noctis/Prompto Arranged Marraige and Objection!
What ever set up or justification you can think of, however it gets to that point, Ardyn is set for an arranged marriage with Prompto. Prompto isn't happy about it, and obviously neither is Noctis or the rest of the chocobros. Who are determined to make sure the wedding doesn't happen. And ultimately have to burst in during the ceremony itself to stop it.