Okay I have a great story here of bitter brothers brought to you by WoL and CK2+..... So here we have the Welf brothers, Hugo and Konrad. They have never liked each other much, but now they are at war and bitterly hate each other.
As a quick background. Here we have the innards of the Carolingian Empire, Louis II became King of Italy, Lotharingia, and Burgundy before his death, but after he died Italy and Burgundy went to his eldest daughter Gisele who had adopted the Italian way of life. Konrad was the Duke of Upper Burgundy and Savoia and was easily the most powerful vassal to the Queen of Italy. After several years though he and the Duke of Dauphine led a rebellion against Gisele and Konrad established his kingship over Burgundy. Meanwhile right next door, his older brother, Hugo had been given the Duchy of Switzerland by me at some point. He was already bitter and jealous of his older brother.
Here are the brothers:
As if it wasn't bad enough being outshines by his older brother, King Konrad began bedding his older brother's wife, the Duchess of Switzerland...
Hugo tried to have his wife, Duchess Wilhelmina imprisoned (or worse), but she made her escape through the alps to the last Lombard kingdom of Salerno in the south of Italy.
So the brothers hate each other and their wives hate each other, there is infidelity on both sides, murder intrigue, and now Konrad, being the never ending douche that he is, has declared war on Hugo for control of the Swiss pass through the alps.
Reminds me of me and my brother (I'm the younger better one).