The name of my site is https://www.example.com, but during a routine check, I've found that along with the usual search results, Google also brought up 1 weird "subdomain" page (a single page) in the results, with an URL like https://w.example.com/page.htm
I found no reference to page.htm in all source code of the page, and also no reference to w.example.com in any of the settings, the Google sitemap or the robots.txt file.
Does anyone have an idea where this strange, "truncated" URL (that is listed along with the results for my site!) may come from? I need to get rid of it.