Rabbits suddenly fighting

We adopted these from the humane society about 6 weeks ago. As far as the shelter knows they're brothers and have always lived together. They're mini Rex, approximately 3 months when adopted. Both neutered. And they seemed very friendly with each other and often snuggling and interacting nicely. They live in a pen but are often out roaming in the living room.

However tonight, they had a big fight. Tufts of fur all over the living room. As far as we can tell, it's the black and white one that's starting the fights by biting and chasing the grey and white one. We separate them for a bit and reintroduce. They're nice for a while and the black and white one starts again.

Any clues as to why? The grey and white one is actually quite a bit heavier than the black and white one, and thus far seemed to be the dominant one, mostly in how he often grooms the black and white one.

Thanks!

We adopted these from the humane society about 6 weeks ago. As far as the shelter knows they're brothers and have always lived together. They're mini Rex, approximately 3 months when adopted. Both neutered. And they seemed very friendly with each other and often snuggling and interacting nicely. They live in a pen but are often out roaming in the living room.

However tonight, they had a big fight. Tufts of fur all over the living room. As far as we can tell, it's the black and white one that's starting the fights by biting and chasing the grey and white one. We separate them for a bit and reintroduce. They're nice for a while and the black and white one starts again.

Any clues as to why? The grey and white one is actually quite a bit heavier than the black and white one, and thus far seemed to be the dominant one, mostly in how he often grooms the black and white one.

Thanks!