domain indexed as subdomain

[maxy22]

I have been using cpanel adon domain feature for many years but never had this problem
today I have noticed that google has indexed one of the adon domains as the subdomain of the domain
why and how did it happen?

[revium]

Not sure how they found it, but maybe it was inadvertently linked from somewhere.

You should block this directory in your robots.txt file. That will solve the problem.