"Aerys is the rightful king! How could you even think of rebelling against him?" He was following Robert from room to room, as Robert gave orders after orders to one knight after another. He would have preferred to have this conversation in private, but Robert would not sit still for one moment, and he was leaving very soon.
He was not sure Robert was even listening, and so was shocked when Robert suddenly shouted. "Out! Everybody out. I need to speak to this clueless brother of mine."
Robert closed the door himself, with a loud thud. Wonderful. Now he can yell even louder. He braced himself for the explosion, but it never came.
"Sit." He heard the brusque command.
"I would rather stand, thank you."
"I am Robert Baratheon, Lord of Storm's End, and your liege lord. And I order you to sit."
He took the seat opposite Robert.
"A green boy of not yet twenty, and you prattle on and on about rightful king and duty and loyalty. What do you know about any of that?" Robert's voice was contemptuous.
"I am not a boy! And you forget, you are only a year older than me. What do you know about those things?"
The explosion finally came. "What do I know? I know that the Mad King's son took Lyanna by force to do who knows what to her. My Lyanna. Ned's only sister. And that "king" you wish to be loyal to, he burned Ned's father alive, and made Ned's brother watch. Do you know how Brandon died? He strangled himself with chains trying to save his father."
Stannis had learned of the deaths, but not the details. "I -"
"He killed Jon's nephew too. Elbert, his heir. And the "king" wants me now. And Ned. He sent a raven to Jon Arryn. Surrender your wards Eddard Stark and Robert Baratheon, or face the consequences. What do you think he means to do with us, dear brother? This "king" you want to stay loyal to?"
I did not know, Stannis despaired. You came home and called the banners and never said anything to me.
How do we know what is our duty? He had asked his father once, back when life was not so complicated. His father had smiled. "You are too young to worry about that", he had answered. But Stannis had insisted. "You know it from the law. And from what is just", his father finally said.
What is the law and justice if the king means to kill my brother? My own flesh and blood.
He was so lost in thought he did not notice that Robert had been watching him silently. Watching and waiting. With a look of disappointment mixed with disgust on his face, Stannis finally realized.
"It took Jon less than a minute to crumple that letter and call his banners. Yet my own blood, he hesitated and hesitated. Forget Lyanna and Ned, or all the dead Starks and Arryn. They mean nothing to you, I know. What about your own brother? Do I mean less to you than some abstract notion of duty and loyalty?"
No, he wanted to scream. You mean more ... but I am who I am, I cannot decide at the drop of a hat. Everything must be considered. But Robert would never understand, he knew. There is an unbridgeable divide between them, a fatal lack of understanding made worse by all the time spent apart.
"Well? Has my dear brother made up his mind yet?"
"If he means to kill you, then all Baratheons are facing the same danger. I will march with you."
Robert snorted. "I suppose self-preservation is as good a reason as any for fighting."
Stannis stifled the urge to respond. Robert will never understand.
"You won't be marching to battle with me. I will be taking most of the men, I can't afford to leave many at Storm's End. I need you to hold the castle. Aerys is sure to send a force to capture Storm's End once the fighting starts. How can I rebel against the throne if I cannot hold on to my own castle, men would say. So you must hold Storm's End for me, no matter what. Will you promise me that?"
He did not hesitate this time. "I promise."
Months and months later, when they were down to nibbling on rat's bones to stay alive, he would remember the look of disappointment mixed with disgust on Robert's face, and his own promise. When Davos slipped through with his onions and salted fish, his first thought had been - I can keep my promise. When Ned Stark came and lifted the siege, his first thought was - I kept my promise.