Attack in the liter box

Hello,
I have two cats they are brothers and have never been separated and have always gotten along really well. However, just recently one of them started to attack the other one while he is in the liter box. I'm kinda worried that this might affect my cats washroom Behaviour what should I do?

If you have 2 male cats, you should have 2 litter boxes. Boys don't care to share. If you can put the second litter box in a different part of the house, that helps, too.
~Morgen