@Daz:
The only reason he didn't know is that the citizens, for some reason, played along with the Royals lies. After the giant fake funeral, people instantly figured out that not-Kyros and not-Scarlet in that house on the hill were in fact Kyros and Scarlet, now having abandoned their home, status and identities to the point where the king needs to sneak out in a disguise to see his own granddaughter.
But I guess it'd be rude of the citizens to tell the couple that they knew? Better let them keep up the lifelong lie for no reason then.
Mabye it wasn't all for the citizens but rather for the country. I mean Dressrosa is suppose to be a peace nation that will do anything to avoid war. To be a shining example for the neighbor islands. But then the royal princess marries a convicted murderer… I mean Dressrosas citizens might be fine with it but what kind example is that to set as a peace nation?