The King and The Prince lived happily ever before, in a great kingdom, where all of it's earlier invasions were because of enemy kingdoms' envy, but they learned their lesson because the last war was like 107 years ago. The King himself was infamous for having a ridiculously large guard, which consisted of knights, crossbowmen, Arabian ninjas etc...
One day a witch came to their castle and asked for food. The King gave her a basket full of bear meat. Too bad the witch was a vegetarian, and she cursed the waters to flood the kingdom after a year for this.
After 10 months, the scribe was able to find the location of future flood - The Holy Peninsula, where the dead come back to life.
With a help of the local monks they were able to finish the stone dam with observation points, to make sure that the flooding will not occur, just in a minute before the flood.
But there was a problem. They realized, that their camp was built on the other side of the dam, and how much they were done for.
Seven days later, the water mostly came down. While all the monks survived by praying, the other weren't so lucky. Besides them, the only survivors were the king, the workers, and 4% of the royal guard, with few of them being stuck on a dam. They soon saw an army far away.
You were standing here. It was your army. The witch was actually a paid mercenary, who only used vegetarianism as a excuse. You saw your son, the bastard who conspired against you and overthrew you, and took the kingdom for himself. Now that they're almost defenceless, you prepare to strike, and reclaim the throne.