When my lad was about 12 and he was big by them, almost my size and I'm not tiny, he was in mid meltdown and squared up to me, raising his hand.
I stood tall and said calmly but firmly "Don't you even think about it!" He backed down and has never done anything of the sort since.
I actually think he remembered when he was 4 he hit me and I made him choose which of his toys he was going to throw in the bin for hitting me. He really didn't think I meant it but I made him put it in the outside bin. He then realised I was serious and burst into tears. It was actually some cheap, crappy toy that he never played with but it had the desired effect.
I then asked the rest of our extended family to express shock and disapproval when I mentioned to them in front of him that he'd hit me. Men that he looked up to like my Dad were very much "Oh no! He didn't hit his Mummy, did he? Oh, we never, ever hit our Mummy"
He's never forgotten it and I'm certain that's why he backed down.
However, when my son got like this, I knew that he was often feeling out of control so I avoided doing anything that would escalate things.
I would be having a chat with your son when he's calmed down and saying that there will be VERY serious consequences if you ever catch him raising a hand/squaring up to his sister or you ever again. Think.of the thing that would be the worst thing for him to lose and then tell him that's what WILL happen.
I'd suggest that if he ever felt that angry again, he can go to his room and punch his mattress or something.