I managed to do this quest in under 2 minutes. Social Empires is a very cool game to kill time with :)please share your strategies, tips & tricks for this game in the comment section below the video. Thanks!
First i set my cannons to attack the towers, then i put my Powerful Archers to kill all Trolls. After all is clear i activate the 4th gem and the super boss fight is on.
I placed the Prince near the Boss and 2 Healers near him so the rest of the army can shoot him.