The story is simple. The video the antagonist was watching was a past video footage of him and the King. The antagonist lost his wife that day. Then the two kingdoms became enemies. Also in that old footage, the king could only save the child of the antagonist. But the antagonist thought he lost both his wife and child.
The king sent out the antagonists child to deliver a treaty. But of course, things went bad. The antagonist ended up killing his own son in a year old grudge against the other kingdom. That's why he was crying when he contacted the King. Because he killed the child he thought he lost years ago.